Degenerative and Compressive Structural Disorders

History and Definitions

Degenerative Structural Disorders

Degenerative Disc Disease

Cervical Spondylosis

Ankylosing Spondylitis

Compressive Structural Disorders

Fibrous Dysplasia

Paget's Disease

Other Compressive Disorders

Compressive Neuropathies

Compressive disorders of the Median nerve

Compressive disorders of the Ulnar nerve

Compressive disorders of the Radial nerve

Thoracic outlet syndrome

Compressive disorders of the Sciatic,Peroneal and Tibial nerves

Other compressive disorders of the lower extremities

HISTORY AND DEFINITIONS

A variety of neurological disorders result from abnormalities of bones, ligaments, muscles, and other mesenchymal tissue that compress the nervous system. In many instances the result is a focal disorder of nervous system function such as a mononeuropathy, a root syndrome, or the compression of intracranial contents by abnormalities of the skull. Much of our clinical knowledge of the peripheral system is derived from these kinds of lesions--for instance, the dermatomal map, which every student of the nervous system carries in his or her black bag, is in part derived from the study of patients with a herniated disc and root compression. Much of the standard neurological examination of the sensory system is derived from studies carried out by Henry Head 80 years ago in patients (including himself) who had lesions of individual peripheral nerves.

DEGENERATIVE STRUCTURAL DISORDERS

Degenerative Disc Disease

Pathogenesis and Pathophysiology. The vertebral disc is composed of the inner gelatinous nucleus pulposus and the surrounding annulus fibrosus. Vertebral disc herniation refers to rupture of the annulus with displacement of the central nucleus. In youth, the disc is highly elastic. With the passage of time, the direct vascular supply to the vertebrae and discs decreases, and they undergo the accumulated effects of axial loading. The resulting decreases in water and oxygen content, and metabolic efficiency lead to a disc that is more compressible, less elastic, and more prone to tear and rupture. Disc rupture and herniation can cause pain by several mechanisms. The periosteum of the bony spine, the ligaments, the outer fibrous annulus of the vertebral discs, and the dura are all innervated by nociceptive afferents from the spinal nerves. A ruptured or torn fibrous disc may generate local pain owing to mechanical stress on these pain-sensitive structures. Also, the exposed disc material has a direct toxic effect and elicits a local inflammatory response, both of which may promote increased pain sensitivity. In addition to these local effects, the mass of the herniated disc material may compress the spinal roots by protruding into the lateral recess or the neural foramen, or it may protrude into the spinal canal, compressing the spinal cord in the cervical or thoracic region or the cauda equina in the lumbosacral region. Details of the mechanisms by which compression causes neurological dysfunction are complex and probably include mechanical alteration of axonal membranes, impaired axonal flow, and ischemia due to compromise of the microcirculation with resultant edema and eventual demyelination. Finally, regional muscle spasm may accompany other effects, adding to the pain and disability.

The accumulation of degenerative lesions in the lumbosacral spine may compromise the area of the central canal available to the cauda equina enough to cause symptomatic lumbar spinal stenosis with or without discrete disc herniation. Most commonly, these lesions include degenerative discs that bulge posteriorly, a hypertrophied ligamentum flavum that bulges anteriorly, and hypertrophied facet joints that crowd into the bony canal posterolaterally. Less common lesions may contribute to the problem, hastening significant stenosis: congenitally short pedicles, spondylolisthesis without spondylolysis, or abnormal angulation of the bony spine.

Epidemiology and Risk Factors. Vertebral disc degenerative changes are a universal accompaniment of aging. Teenagers rarely develop symptomatic disc herniation. The peak incidence of symptoms occurs between the ages of 30 and 50. Patients often describe the onset of low back pain, usually remittent and without specific features, in their twenties, perhaps after identifiable trauma, and the onset of more specific symptoms that leads to the diagnosis of disc herniation is often not preceded by further trauma. Probably the accumulation of degenerative changes to the annulus and the preservation of the expansile gelatinous nucleus, overlapping with a period of life when job and sports-related activities increase the amount of mechanical stress on the body, account for this peak in the incidence of disease. The incidence then falls off in the older population, probably due to the lack of mobility of the desiccated disc and the relative lack of physical activity. Women and men are affected approximately equally.

There is a tendency toward disc herniation in some families, such as those with congenital spinal anomalies, including fused and malformed vertebrae and lumbar spinal stenosis due to short pedicles. Patients with increased weight and tall stature are at increased risk for this condition. Also, acquired spinal disorders, such as common degenerative arthritis and ankylosing spondylitis, predispose to disc degeneration. Various behaviors that increase risk include sedentary occupations, physical inactivity, motor vehicle use, vibration, and smoking. In younger women, pregnancy and delivery are associated with lumbosacral herniation, and new symptoms of cervical disc herniation may occur in part because of the bending and lifting involved in child rearing.

Clinical Features and Associated Disorders. The most common site of disc herniation in the cervical region is the C6-C7 level, followed by C5-C6, C7-T1, and C4-C5. Patients typically develop some local pain in the neck that radiates to the shoulders or the interscapular region. In the most common lateral herniations, radicular symptoms ensue. These symptoms include pain in the shoulder and arm, which may follow a dermatomal pattern but more typically is deep and aching and only roughly corresponds to the involved dermatome. At the cervical levels, the roots emerge laterally to exit through the neural foramina above the correspondingly numbered vertebral bodies. Because the spinal cord and bony vertebral levels are roughly aligned in the neck, the level of herniation corresponds to the level of root irritation. Hence, C6-C7 herniation affects the C7 root. Pain may be exacerbated by coughing or straining. Numbness is more likely to supply reliable localizing information than pain. Compression of the C6 root typically causes numbness in the thumb and index finger, and compression of the C7 root typically involves the index and middle fingers. When compression is severe, myotomal weakness, reflex loss, and, with time, fasciculations and atrophy may ensue. With C6 compression, the biceps, brachioradialis, pronator teres, and radial wrist extensors may be weak, and the brachioradialis and biceps reflexes may be diminished or lost. With C7 weakness, the wrist and finger extensors and the triceps are typically weak. The triceps reflex may also be diminished or lost. With C8 compression, there is often interscapular pain and pain in the medial aspect of the arm and hand with weakness of the hand intrinsic muscles. The finger flexor reflex may be lost. Lesions above C6 are less common and are associated with correspondingly more proximal sensory symptoms and weakness. Lesions of the C5 root may cause shoulder pain and pain and numbness in the lateral aspect of the upper arm. Many muscles can be used to test the C5 root, including the infraspinatus, supraspinatus, deltoid, biceps, and supinator. Lesions above this level may cause neck pain and sensory loss in the neck, supraclavicular area (C3), and acromioclavicular area (C4) of the shoulder. Lesions involving the spinal cord or roots above C4 may paralyze the diaphragm and cause respiratory compromise ( Table 29-1 ).

In the lumbosacral region, the most common site of

TABLE 29-1 -- CERVICAL RADICULOPATHIES

Root

Muscle Weakness

Action

Location of Pain

Reflex Change

C5

Deltoid

Shoulder abduetion (15-90 degrees)

Lateral shoulder

Biceps

Biceps

Elbow flexion

Lateral upper arm

Supraspinatus

Shoulder abduction (0-15 degrees)

Lateral epicondyle

Infraspinatus

Humerus external rotation

C6

Brachioradialis (C5-C6)

Elbow flexion in semipronation

Posterior shoulder

Brachioradialis

Pronator teres (C6-C7)

Pronation

Lateral forearm

ECR (C6-C7)

Radial wrist extension

Thumb and index finger

C7

Triceps (C6-C8)

Elbow extension

Posterior shoulder

Triceps

ECR (C6-C7)

Radial wrist extension

Medial forearm

ED (C7-C8)

Finger extension

Index and middle fingers

C8

Flexor pollieis longus

Thumb flexion

Interscapular medial forearm

Finger flexors

FDS, FDP

Finger flexion

Little finger

T1

Interossei

Finger abduction

Medial forearm

None

Abductor digiti minimi

Little finger abduction

Medial epicondyle

ECR, Extensor carpi radialis; ED, extensor digitorum; FDS, Flexor digitorum superficialis; FDP Flexor digitorum profundus Actual motor innervation is multisegmental. Most of the myotomal overlap is disregarded here to emphasize clinically useful localization.


herniation is the L5-S1 level, followed by the L4-L5 level and then higher levels. Symptoms of lumbosacral herniation often follow lifting or twisting injuries, or they may result from accumulated low-level trauma. Pain typically occurs in the parasacral area and radiates to the buttocks. Below C8, the roots exit through the neural foramina below the correspondingly numbered vertebral bodies. In patients with the most common posterolateral herniation, dermatomal radicular pain typically occurs at the level below the emerging root, which usually escapes entrapment above the protruding disc. Hence, L4-L5 herniation affects the L5 root . With posterolateral L5-S1 herniations and S1 root entrapment, the pain radiates to the posterior aspect of the thigh and, especially when the root is stretched, into the posterolateral lower leg, lateral heel, and sole. This pattern can be demonstrated by straight-leg raising, in which the smaller the angle of elevation required to elicit pain, the greater the suggestion that root compression is responsible.
Characteristic pain on Some patients with symptoms elevation of the opposite leg may be even stronger evidence of root compression. that are exacerbated by root traction avoid full weight bearing on the heel of the involved side, standing with the knee flexed and the heel off the floor. When pain is less severe, symptoms may be elicited by having the patient walk on the heels. Numbness is felt in the posterolateral leg, lateral aspect of the heel, and the sole of the foot. The gastrocnemius and hamstrings may be weak, and the ankle jerk may be diminished or lost. More lateral herniation of the L5- S1 disc or herniation of the L4-L5 disc may entrap the L5 root. Here the pain may be similar, with adjustment of the findings to fit the L5 dermatome and myotome. Numbness is most marked on the dorsum of the foot. Weak muscles include the foot elevators (tibialis anterior group), everters (peronei), and invertors (tibialis posterior), and the toe extensors (extensor hallucis longus). Herniations at higher levels in the lumbosacral region cause pain and deficits that correspond to the roots involved ( Table 29-2 ).

In addition to these radicular syndromes, patients with central herniations in the cervical or thoracic region may develop pain and acute myelopathic symptoms with spasticity and quadriparesis or paraparesis, sensory loss at or below the segmental dermatome of the lesion, hyperactive reflexes, and Babinski's signs. Soon after an acute lesion develops, the reflexes may diminish because of spinal

 

TABLE 29-2 -- LUMBOSACRAL RADICULOPATHIES

Root

Muscle Weakness

Action

Location of Pain

Reflex Change

L1

Iliopsoas (sometimes, but mainly L2-L3)

Hip flexion (mainly L2-L3)

Inguinal crease

None

L2

Iliopsoas (L2-L3)

Hip flexion

Anterior and lateral thigh

Cremasteric

L3

Adductor group

Hip adduction

Medial thigh and knee

Knee

Quadriceps

Knee extension

L4

Quadriceps

Knee extension

Medial lower leg

Knee

Tibialis anterior

Foot dorsiflexion

Medial malleolus

L5

EHL, EHB

Great toe extension

Anterolateml lower leg

Tibialis posterior

EDL, EDB

Toe extension

Dorsum of foot

Internal hamstrings

Tibialis anterior

Foot dorsiflexion

Peroneii

Foot eversion

Tibialis posterior

Foot inversion

Gluteus medius

Hip abduction

Internal hamstrings

Knee flexion

S1

Biceps femoris

Knee flexion

Lateral heel

Ankle

Gastrocnemius soleus

Foot plantar fiexion

Sole of foot

FDB

Toe flexion

Gluteus maximus

Hip extension

EHL, Extensor hallucis longus; EHB, extensor hallucis brevis; EDL, extensor digitorum longus; EDB, extensor digitorum brevis; FDB, flexor digitorum brevis Actual motor innervation is multisegmental. Most of the myotomal overlap is disregarded here to emphasize clinically useful localization.


shock. Patients with lumbosacral central herniation may develop acute compression of the cauda equina. This causes radicular pain, paresthesias, and sensory loss referable to multiple bilateral roots, bilateral leg weakness, and loss of the lower extremity reflexes. Bowel and bladder dysfunction may occur early. When subtle, this dysfunction may be limited to asymptomatic bladder retention noted only on postvoid catheterization. When dysfunction is more severe, there may be perianal and perineal sensory loss, loss of anal tone and reflexes (the reflex anal sphincter constriction due to perianal skin stimulation or anal wink and the bulbocavernosus reflex), and fecal and urinary retention and incontinence.

Degenerative herniations in the thoracic region are uncommon, and symptoms and findings at these levels should raise a suspicion of other underlying lesions, such as tumor or abscess. Disc herniations at this level may cause radiating dermatomal pain resulting from root compression; more frequently, they progress to spinal cord compression.

The symptom most suggestive of lumbar spinal stenosis is neurogenic claudication. Low back pain radiates to the buttocks and thighs and may extend more distally along the lumbosacral dermatomes. This pain is brought on by walking. Unlike vascular claudication, rest in the upright position does not relieve the pain, but rest while seated or forward bending, such as leaning on a shopping cart, may provide relief. Pain is exacerbated by spinal extension, such as downhill walking. When spinal stenosis is severe, patients bend forward while walking. Symptoms and signs may be either mechanical, due to bone, ligament, and joint involvement, or radicular, due to compromise of the lateral recesses or neural foramina.

Proximal compression resulting from root entrapment may increase the vulnerability of nerves to dysfunction due to distal entrapment. This double crush phenomenon is presumed to be a result of disturbed axoplasmic flow and disrupted architecture of the neurofilaments. Therefore, when surgical repair of a distal entrapment fails to provide the expected relief, a contributing radiculopathy resulting from degenerative disc disease should be considered.

Differential Diagnosis. Disc herniations must be differentiated from other causes of acute and chronic neck, back, and extremity pain, radiculopathy, and myelopathy. Malignant and benign tumors affecting the spine, infection, epidural hematoma, various arthritides, including rheumatoid arthritis, ankylosing spondylitis, and Reiter's syndrome, and other spondyloarthropathies may present with similar early symptoms and signs. Various anomalies, such as conjoined spinal roots and multiple roots emerging through a single foramen, may also be confused with disc disease. Degenerative arthritis of the spine can cause symptoms by many mechanisms, including disc herniation, and the various lesions that are causing symptoms in a particular person should be differentiated as clearly as possible to allow directed therapy.

Evaluation. A careful history and physical examination are critical in the evaluation of disc herniation. It has been well established with all imaging modalities that asymptomatic patients have a high incidence of anatomical lesions. To properly detect clinically relevant illness, it is therefore essential to establish the closest possible clinical correlation of the symptoms and signs with the anatomical findings of the various imaging studies. The initial history should screen for problems that raise a suspicion of severe underlying disease. All patients should be questioned about trauma, cancer, infections, recent fever, and the use of anticoagulant medications. The underlying family history and risk factors for tumor, infection, hematoma, and various disorders that predispose to disc disease should be sought. The physical examination, likewise, is undertaken to seek evidence of other severe underlying disease and to localize and classify the pain and any deficits as mechanical, radicular, or myelopathic. It is most important immediately to establish the presence of major deficits that demand rapid diagnosis and treatment. These include the cauda equina or conus syndrome, acute or progressive myelopathy, and severe radicular motor deficits. If, on the other hand, the findings are consistent with a ruptured disc and either no deficit or a mild to moderate one, it is reasonable to temporize before pursuing a workup to fully evaluate the cause. If plain radiographs of the affected area reveal no evidence of unexpected lesions, conservative therapy for disc herniation may be tried before further imaging is performed. This approach is justified by the good prognosis for spontaneous recovery of patients with acute radiculopathy with mild to moderate deficits. When the clinical examination leaves doubt about the localization of the lesion, electromyography (EMG) can supplement the diagnosis of radiculopathies and suggest other localizations, such as plexopathies and neuropathies. Electromyography is more sensitive if it is delayed until at least 10 to 14 days after the onset of a new deficit.

The tests available for imaging include plain radiographs, computed tomography (CT), myelography with or without CT, and magnetic resonance imaging (MRI). X-ray studies can be used to screen for unexpected infection, tumor, or deformity of the bony spine. Radiographs cannot show the neural tissues or the disc itself, but loss of disc space height and other degenerative changes may provide some indirect diagnostic information. Interpretation of plain radiographs must be tempered by an awareness of the high frequency of degenerative findings in asymptomatic populations. Plain radiographs taken under conditions of flexion and extension can also be used to assess spinal stability. Myelography is invasive, indirect, and nonspecific; however, it retains certain advantages in the era of MRI. It can visualize the entire length of the spine and best defines the root sleeves. Although myelography alone cannot distinguish between osteophytes and a herniated disc compromising a foramen, when combined with CT, it provides the best visualization of lateral pathology and small osteophytes. It is now most commonly used to answer specific questions that remain after the MRI examination. CT is superior to MRI in distinguishing soft tissue from bone. MRI has emerged as the preferred imaging choice in most cases. It demonstrates bone and soft tissues directly, easily allows multiplanar visualization, and is suited to the visualization of multiple levels. The high contrast of epidural fat and the cerebrospinal fluid (CSF)-filled thecal sac allows accurate assessment of subtle compression in most cases.

Lumbar spinal stenosis is evaluated by CT or MRI. MRI best demonstrates the relationship of the bony and neural structures. CT best demonstrates lateral recess stenosis. Although the dimensions of the bony canal can be used as guidelines, diagnosis must ultimately be based on the correlation of stenosis with the clinical findings. The transverse interfacet dimension should be greater than 16 mm. A dimension of less than 10 mm indicates severe stenosis. An anteroposterior dimension of less than 12 mm suggests stenosis; however, this finding is less sensitive in patients with symptomatic disease. A lateral recess of 3 mm or less suggests stenosis.

Management. The crucial initial step in management of patients with disc herniation syndrome is to identify those lesions that merit further evaluation and immediate therapy. In the remaining cases, the good prognosis for early recovery justifies a trial of conservative therapy before definitive imaging is done. Conservative therapy includes rest in a position of comfort followed by early remobilization, gentle exercises, and analgesics for pain as needed. Nonsteroidal anti-inflammatory agents probably provide little relief in most cases. For severe pain, judicious time- limited use of narcotics should be considered. Oral and epidural corticosteroids can be helpful. Many other modalities are available, but there are few reliable data about their effectiveness in populations: medical and physical measures (e.g., ice, heat, massage, and ultrasound) that address secondary muscle spasm, transcutaneous electrical nerve stimulation (TENS), acupuncture, exercise, and traction. If improvement within the initial 4 to 6 weeks is not satisfactory, it is helpful to confirm the diagnosis by imaging. This may provide a diagnosis of an unsuspected condition, localization for epidural steroid injection, or information about suitability for eventual surgery.

Clear indications for surgery include the presence of acute myelopathy, cauda equina syndrome, severe or progressive motor deficits, and intractable pain. When conservative measures fail to provide a satisfactory response within 6 to 12 weeks, surgery should also be considered. Studies comparing the outcome of surgical therapy with conservative care suggest that early recovery occurs more often with surgery. Although the benefits of surgery are lost with prolonged follow-up periods, it is important to point out that in an often cited study, patients in the conservative therapy group who had not responded to this therapy received surgery. Newer microsurgical techniques allow shorter hospitalization and rehabilitation periods but have not been shown to improve long-term outcome. The success rate of chymopapain chemonucleolysis has not reached that of surgery in most hands, and this treatment carries significant risks. Percutaneous nucleotomy has also been disappointing and should not be pursued given the current level of experience.

For patients with lumbar spinal stenosis, initial therapy is symptomatic, with analgesics, pain-modulating medications, and physical and occupational therapy. When significant disability and pain remain despite conservative measures, referral for surgical decompression should be considered.

Prognosis and Future Perspectives. The prognosis for the relief of pain and a full functional recovery is good. With bed rest alone, Weber found that 70 percent of patients experienced decreased pain and improved function within 4 weeks, and 60 percent had returned to work. Seventy percent were functionally unrestricted at 1 year. With selective surgery, 90 percent of patients should have a good functional recovery within a year. Patients with psychosocial problems tend to do worse with either therapy, but those with appropriate indications respond better to surgery. Sensory dysfunction does not recover as fully as motor function, and a large proportion of patients retain some sensory deficits. Patients in whom relapse occurs should be re-evaluated for new lesions that are potentially addressable by surgery; however, the success rate of surgery declines with follow-up procedures, and a significant proportion of patients with disc herniation experience relapse with chronic low back pain.

Research into the mediators and biomechanics of pain may further elucidate the mechanisms of pain in disc disease and provide other conservative therapies. Improved imaging techniques may further refine the selection of patients for surgery. It is hoped that improved surgical selection and further refinements in surgical technique may continue to improve outcome and shorten the period of disability.

Cervical Spondylosis

Pathogenesis and Pathophysiology. Degenerative changes of the spine universally accompany aging, and the accumulation of such degenerative changes in the cervical spine constitutes cervical spondylosis. These spondylotic changes become clinically important when they cause pain or neurological dysfunction. Aging leads to desiccation and shrinkage of the intervertebral discs. The resultant loss of vertebral height narrows the intervertebral foramina. The weakening of the containing fibrous annulus allows bulging of the desiccated discs, which may then form transverse bars that protrude posteriorly, compromising the spinal canal. Their protrusion more laterally into the foramina may further compromise this space. Osteophytes and hypertrophic osteoarthritic changes of the facet and uncovertebral joints may further impinge on the spinal canal and foramina. Hypertrophy of the ligamentum flavum, which runs longitudinally along the posterior wall of the spinal canal, may compromise this space even more . Intuition suggests that compression of the cervical spinal cord and nerve roots by the stenosis of the spinal canal and foramina is responsible for the myelopathy and radiculopathies characteristic of cervical spondylosis. However, a finer understanding of the pathogenesis of this disorder has been elusive. Proposed explanations of the neurological deficit include (1) direct compression by stenosis adequate to compromise the cord and roots, (2) rubbing of the spinal cord and roots on protruding skeletal structures that may not themselves be severely compressive, and (3) arterial or venous compromise. All of these factors may play a role. Pathological study shows the presence of distorted and flattened spinal cords that correspond to spondylitic bars. Demyelination of the lateral columns occurs at the stenotic site and caudally and of the posterior columns rostrally. This demyelination corresponds to the sites of rubbing: anteriorly and inferiorly with neck flexion and posteriorly and superiorly with extension. In the central gray matter ischemic changes with neuronal loss are seen. Sometimes syringomyelia can be found. Root sleeves may be thickened and rootlets adherent.

Epidemiology and Risk Factors. The major risk factor for cervical spondylosis is aging. Although trauma may contribute, there is usually no history of significant trauma. Screening of asymptomatic patients shows a high frequency of spondylotic changes that increases with advancing age. By age 59, 70 percent of women and 85 percent of men have changes on radiographs, and by age 70, the number increases to 93 percent of women and 97 percent of men. Up to 75 percent of these patients have abnormal neurological findings by age 65, but fewer have symptoms of spondylosis. Heavy labor and especially occupations that expose the patient to vibration probably increase the risk of spondylosis.

Clinical Features and Associated Disorders. The major clinical features are the symptoms and signs referable to cervical myelopathy and radiculopathy. Patients may complain of neck pain and pain radiating into the arms. There may be weakness of the legs and sensory loss, especially of position sense. The weakness or sensory loss may be discovered when an elderly patient presents for gait problems or falls rather than as a direct complaint. Bowel and bladder dysfunction are uncommon complaints accompanying advanced cervical myelopathy. Most commonly, the onset of symptoms is insidious; however, occasionally an elderly patient with spondylosis presents with catastrophic onset of quadriparesis or paraparesis after a fall.

Typically, there is some limitation of neck mobility. Examination of the cranial nerves should be normal, although the jaw jerk may be increased in some cases. Weakness is common in the lower extremities, especially in the iliopsoas, hamstrings, and extensors of the feet and toes. Tone in the lower extremities is spastic, and Babinski's sign may be present. Sensory loss to light touch, vibration, and joint position is sometimes found. The major deficits in lower extremity function are determined by the degree of myelopathy. Findings in the upper extremities vary depending on the level of central canal stenosis and the degree of cervical root involvement. Patients may have mild weakness with brisk reflexes. When roots are compromised, especially in the lower cervical myotomes, atrophy, weakness, and fasciculations may be found, at times mimicking the signs of amyotrophic lateral sclerosis. Sensory loss in the upper extremities may also be seen, following a simple radicular pattern or, more commonly, a patchy distribution, presumably due to multiple root and cord involvement.

The main associated features are those of disorders that compromise the cervical spine and predispose to osteoarthritis. These include prior trauma, prior disc herniation, various congenital anomalies of the cervical spine, and underlying systemic arthritic disorders.

Differential Diagnosis. The issue of differential diagnosis is particularly important when one is dealing with a condition that is commonly present as an asymptomatic radiological finding. When a patient presents with a combination of radicular signs and symptoms accompanied by cervical myelopathy, the diagnosis of spondylotic disease is not difficult. However, this clinical presentation is not common, and most patients have either myelopathy resulting from central protrusions or radiculopathy resulting from lateral protrusions, but not both. The differential diagnosis must therefore cover conditions that cause pure myelopathy, motor neuron disease, and combined myelopathy and radicular or neuropathic lesions.

The syndrome of slowly progressive spastic weakness of the extremities, worse in the lower than in the upper extremities, may be produced by a variety of pathological causes. Some of these are listed here along with clues that may help to distinguish them from spondylotic myelopathy.

Multiple Sclerosis Age of onset, gender, and types of neurological findings do not reliably distinguish chronic spinal multiple sclerosis. Early onset of bladder symptoms, visual complaints, and mental status changes should be sought. Cranial MRI may demonstrate periventricular bright lesions on T2-weighted images in the majority of patients with multiple sclerosis. Visual evoked responses and oligoclonal bands in the CSF, if abnormal, are helpful.

Amyotrophic Lateral Sclerosis In most patients with amyotrophic lateral sclerosis, lower motor neuron signs are evident from the beginning, but spasticity predominates in a few. The finding of atrophy of muscle and increased reflexes in the same myotome strongly suggests amyotrophic lateral sclerosis. Bulbar symptoms or signs should be carefully sought on examination and should be evaluated with EMG. The sensory loss from radicular or long tract involvement, common in cervical spondylosis, should be absent. In one recent series, 5 percent of patients with amyotrophic lateral sclerosis underwent a cervical laminectomy in the hope of arresting progressive spasticity, emphasizing how commonly the two conditions coexist.

Primary Lateral Sclerosis. A few patients with a slowly progressive, purely spastic condition are found to have a degenerative disease allied to amyotrophic lateral sclerosis, but without lower motor neuron features.

Subacute Combined Degeneration of the Spinal Cord Vitamin B12 deficiency should never be overlooked. A low serum B12 level, hypersegmented polymorphonuclear leukocytes, and macrocytic anemia are some of the abnormalities found in early cases. The lesions of B12 deficiency begin in the cervical or thoracic cord, and deficits are often primarily sensory, which is quite uncommon in patients with cervical spondylosis.

Dural Arteriovenous Fistula.Several decades ago it was believed that spinal arteriovenous malformations presented either as subarachnoid hemorrhage or as the lumbar syndrome of painful cauda equina deficit. It is now known that small arteriovenous fistulas in the spinal dura can cause myelopathy with either a stepwise progression or abrupt onset. Most malformations are seen on MRI or myelography; however, some require selective angiography of the segmental arteries that supply the cord for definitive diagnosis.

Myelopathy Associated with AIDS A subacute vacuolar change in the spinal cord may develop in patients with human immunodeficiency virus (HIV) infection, usually in those with frank acquired immune deficiency syndrome (AIDS) and a history of multiple opportunistic infections. Most patients are younger than the average patient with spondylosis. The clinical findings often emphasize an ascending sensory disorder.

HTLV-I Myelopathy A slowly progressive spastic paraparesis with early bladder involvement in a patient from a region endemic for human T-cell leukemia-lymphoma virus (HTLV)-I infection should prompt suspicion of this infectious cause. Patients typically have milder spasticity of the upper extremities. Diagnosis can be made by identifying the presence of antibodies to HTLV-I in serum.

Familial Spastic Paraplegia. These patients can be recognized by their family history, usually that of an autosomal dominant disorder. No direct DNA testing is available.

Syringomyelia. Cervical syringomyelia may occur in isolation or in association with the Chiari malformation, trauma, or tumor. Patients typically have lower motor neuron signs in the upper extremities due to involvement of the central gray matter and upper motor neuron signs in the upper and lower extremities due to involvement of the descending corticospinal tracts. The segmental loss of spinothalamic modalities of sensation and the neuropathic quality of the accompanying neck, back, and extremity pain as well as the context of an associated underlying problem suggest the diagnosis. MRI demonstrates the syrinx.

Compressive Lesions at the Craniocervical Junction. The Chiari malformation may cause myelopathy, vertigo, and ataxia. There may be an associated syringomyelia. Basilar impression due to instability of the atlanto-occipital joint or atlantoaxial instability, as in rheumatoid arthritis, may cause slowly progressive myelopathy. These lesions often occur in the context of spondylotic lesions, and it is very important to clarify the source of progressive findings. Certain tumors, such as meningiomas and schwannomas, at the craniocervical junction may also mimic the signs of cervical spondylosis. Often the history suggests a loss of function on one side followed by progression of signs to all four extremities. Down-beating nystagmus suggests the localization. Imaging high enough to demonstrate the craniocervical junction is crucial before cervical myelopathy is attributed to spondylotic lesions.

Evaluation. Evaluation begins with a careful history and examination. This is especially important because of the known high rate of radiological spondylotic abnormalities in asymptomatic populations. It is very important to establish the best possible correlations between the clinical findings and the imaging abnormalities. Available imaging modalities include plain radiographs, CT myelography, and MRI. Plain films can show many of the degenerative changes of bony elements; however, they do not reveal the relationship of these to the neural structures. Simple flexion and extension films performed with care can also demonstrate spinal instabilities that are not apparent on MRI or CT myelography. MRI is the easiest noninvasive means of diagnosis. MRI can demonstrate the dimensions of the spinal canal and foramina and distortion of the spinal cord and roots caused by the impingement of bony structures. Gadolinium enhancement can demonstrate the presence of various alternative lesions that may be under consideration. CT myelography can be used to answer any questions that remain after MRI. The myelogram may fail to show complete block even when significant spondylotic myelopathy is present.

Management. Conservative management of cervical spondylosis includes immobilization with a cervical collar and the use of non-narcotic, nonsteroidal medications for pain. The symptoms and signs in most patients stabilize with this therapy; that is, the myelopathy does not progress, and in some patients it improves. Yet controlled studies evaluating the benefit of immobilization have not been done. When radicular pain is the major problem demanding further intervention, epidural steroid injections can be effective. We refer patients for neurosurgical evaluation and surgical therapy when their myelopathy progresses despite these conservative measures, after careful consideration of other diagnostic possibilities as listed earlier. There has been no documentation of long-term benefit from surgery, although many series have shown evidence of benefit in the short term. Posterior decompressive laminectomy is the procedure that has the longest history. However, unless it is performed over many levels, it will not relieve multilevel compression. Wide decompression performed over a number of segments may be complicated in later years by a swan neck deformity owing to the loss of posterior supporting elements. The anterior approach with interbody fusion is especially suitable for patients with single level nerve root compression. Its benefits for cord compression are less well defined. When radicular symptoms are due to bony osteophytes, foraminotomy may relieve the symptoms and signs of root compression. Although the benefit of surgery has not been systematically validated, and many patients improve spontaneously or with immobilization by a collar, clinical experience with individual cases suggests that selected patients do benefit and show marked improvement shortly after decompressive surgery.

Prognosis and Future Perspectives. The natural history of cervical spondylosis is not known. Although the course of the disease is progressive and most patients have chronic symptoms, the large majority remain stable for many years and do not require surgical intervention.

MRI has greatly advanced the precision of diagnosis while sparing most patients the discomfort and risk of myelography. Future advances in imaging may further facilitate diagnosis. Rowland has pointed out our great lack of knowledge of the natural history of cervical spondylosis as well as the need for controlled trials to demonstrate the effects of surgery and clarify surgical indications. Such studies, if they are done, will require a cooperative effort and careful definition of clinically relevant questions.

Ankylosing Spondylitis

Ankylosing spondylitis (AS) is one of the group of seronegative forms of arthritis, which also includes Reiter's syndrome and psoriatic arthritis. There is a close association with the HLA-B27 type, and the disease is more than three times more common in men than in women. In many patients, the disease seems to progress slowly for years, primarily with back pain, and then stabilizes without much disability. In some cases the disease progresses to total spinal fusion, producing a typical bamboo spine on x-ray criteria. In all patients, the presence of sacroiliac joint disease on radiographs is required to make the diagnosis. There are two major neurological complications of AS: a cauda equina syndrome of unclear etiology, and several types of cervical spinal cord compression due to dislocation or deformity.

Ankylosing spondylitis is less common in black populations and in people of Japanese ancestry, in parallel with the lower expression of HLA-B27 in these groups. There is a considerable familial incidence of AS. Approximately 20 percent of patients with AS have joint disease in the peripheral joints, not in the vertebral column or pelvis, and it is in this group that the neurological complications seem to be most frequent.

Patients with the cauda equina syndrome of AS have a gradual and relatively symmetrical loss of function in the L5, S1, and S2 roots. Both motor and sensory fibers are affected. Foot drop, weakness of plantar flexion, and perianal sensory loss are typical. Nearly all patients develop bladder and bowel incontinence. The cervical spine disorder most often associated with AS is instability at the craniocervical junction because of ligamentous laxity at the level of the odontoid process. Some patients have stepwise subluxation of the cervical spine, resembling that seen in seropositive rheumatoid arthritis. In either case, myelopathy may develop, often with significant sensory loss in the hands, as well as quadriparesis. As in rheumatoid arthritic disease, there may be marked instability of the cervical spine or craniocervical junction with much local pain, sudden changes in neurological symptoms with postural change, and eventual requirement for surgical fusion. Patients with AS may have uveitis or cardiac disease. Fractures of the fully or partially fused spine, especially if osteopenia exists, are common.

The cauda equina syndrome can be confused with lumbar disc disease, but the distinguishing features of the former are symmetry and early loss of bladder function. The craniocervical instability of AS produces a myelopathy that may be insidious and difficult to distinguish from general weakness, myopathy, nerve entrapment, or generalized neuropathy.

The diagnosis should be confirmed radiologically; there are specific criteria for the diagnosis of AS. Cauda equina syndrome is accompanied by a distinctive radiological change, consisting of a wide patulous distention of the subarachnoid space in the sacral region, often with erosion of the overlying sacral bone. The cause of this distended space is unknown, nor is it clear how this distention contributes to nerve root dysfunction. CSF examination does not suggest an arachnoiditis. The cervical spine should be fully visualized by MRI, and the position of the odontoid should be carefully noted. In rheumatoid arthritis patients, asymptomatic widening of the space between the odontoid and the arch of C1 (normally 3 mm or less) is observed. In AS, unrecognized fracture, odontoid dislocation, or atlantoaxial dislocation can occur.

Unfortunately, no specific therapy is available for patients with the cauda equina syndrome. A scattering of case reports indicate that some authors have attempted decompression of the thecal sac. Decompressive laminectomy is of no value. Fractures or cervical dislocations may require fusion.

COMPRESSIVE STRUCTURAL DISORDERS

Fibrous Dysplasia

Pathogenesis and Pathophysiology. Our understanding of the pathogenesis of fibrous dysplasia has advanced greatly in recent years. Several investigators have identified a point mutation in the gene that codes for the alpha subunit of the G-protein, Gsa, in affected bone and other tissues in patients with fibrous dysplasia. The absence of this mutation in non-affected tissues in patients with the disease suggests that a somatic mutation occurs early in embryogenesis to create a genetic mosaic. The mutated Gsa proteins activate adenylate cyclase and increase signaling through the cyclic adenosine monophosphate (cAMP)- protein kinase A pathway. Recent work suggests that the resultant phosphorylation of transcription factors enhances transcription of the proto-oncogene c-fos and translation of c-fos protein in affected tissues. These findings surely represent only part of the molecular story, and it is likely that enhanced production of other oncoproteins is yet to be discovered. These molecular changes result in a gain of function that probably underlies the bony and endocrinological lesions characteristic of fibrous dysplasia. The functional result is a disorder of lamellar bone remodeling and repair. The pathological result is a replacement of normal bone and marrow elements by a vascular fibrous tissue composed of whorls of proliferating fibroblasts with haphazardly arranged trabeculae of metaplastic bone and fluid-filled cystic areas lined by multinucleated giant cells. The appearance is similar to that of osteitis fibrosa cystica due to hyperparathyroidism but is distinguished by the absence of osteoblasts. The abnormal bone originates from the medullary cavity and grows outward thinning the bony cortex. The high prevalence in puberty, the accelerated expansion of lesions during pregnancy, and the association with precocious puberty in females in the McCune-Albright syndrome , suggest a hormonal influence that is, so far, poorly understood. Estrogen and progesterone receptors have been identified in affected bone. Patients with fibrous dysplasia have an accelerated turnover of bone, and many have elevated serum alkaline phosphatase levels, reflecting increased osteoblastic activity. Those with extensive disease also have elevated urinary hydroxyproline, reflecting increased turnover of collagen, a measure of the activity of osteoclasts. Serum calcium and inorganic phosphorus remain normal, reflecting compensatory increases in bone formation and resorption. Fibrous dysplasia is generally considered to occur sporadically. Sassin and Rosenberg found no positive family histories among 50 cases with cranial fibrous dysplasia. This result is consistent with the current hypothesis that the disorder results from a somatic mutation early in embryological development.

Epidemiology and Risk Factors. The age of onset is variable, but the disorder most commonly presents in childhood, especially during the period of most rapid bone

TABLE 29-3 -- FREQUENCY OF SKULL BONE INVOLVEMENT OF SKULL BONE BY FIBROUS DYSPLASIA

Bone

Number of Cases

 

(N = 50)

 

Frontal

28

 

Sphenoid

24

 

Frontal and sphenoid

18

 

Optic canal involved

10 (3 bilateral)

 

Temporal

8

 

Parietal

6

 

Occipital

2

 

Adapted from Sassin JF, Rosenberg RN: Neurological complications of fibrous dysplasia of the skull. Arch Neurol 1968;18:363-369.

 


growth. However, in one series of 50 patients with fibrous dysplasia of the skull, over half came to medical attention after age 18. There is no difference in incidence based on race or sex for the most typical forms.
However, the McCune-Albright syndrome occurs more frequently in females. As noted earlier, the bony lesions may expand at an accelerated rate during pregnancy.

Clinical Features and Associated Disorders. About 70 percent of patients have the monostotic form involving a single bone. The remainder have the disseminated polyostotic form, which is often predominantly unilateral. Sites of involvement vary, the ribs and long bones being the most common sites. The skull is involved in about 50 percent of polyostotic cases and in 10 to 27 percent of monostotic cases. Most of the clinical manifestations that prompt neurological evaluation are due to skull involvement ( Table 29-3 ). Patients may present with a variety of focal neurological findings secondary to the compressive effects of the involved bone . Visual impairment followed by hearing loss and tinnitus are the most common presenting neurological deficits. Although various other cranial neuropathies may occur as a result of the compressive effects of involved bone, these are rare enough that none were seen in two large studies of cases involving the skull. , 20 Optic nerve compression with visual symptoms is common when the frontal and sphenoid bones are involved. A proptotic and downward displaced eye is often seen when these bones are involved and should prompt questions about visual symptoms and a radiological evaluation of the optic canal. Patients with stenosis of the optic canal may complain of decreased acuity or blurring of vision, scintillating scotoma, flashing light, or graying of vision when pressure is applied to the globe. Optic atrophy may be seen on funduscopic examination. The visual symptoms may be slowly progressive, and they have often been present for some time when the patient presents. Patients may also have progressive facial asymmetry and deformity resulting from facial nerve involvement. Patients with hearing deficits typically have conductive loss due to stenosis of the external canal and middle ear by the involved temporal bone. A nonthrobbing headache may be a common complaint as well. Sassin and Rosenberg's patients also had an increased incidence of seizures (6 of 50), confirming the findings of prior reports. The reason for this association is not known.

Fibrous dysplasia has been associated with various other disorders. Cutaneous pigmentation occurs in over 50 percent of those with the polyostotic form. The McCune- Albright syndrome consists of polyostotic fibrous dysplasia, usually largely unilateral, with cafe(c) au lait spots, and various forms of endocrine hyperfunction, especially precocious puberty in females. , Rarely, other endocrine abnormalities, including hyperthyroidism, acromegaly, Cushing's syndrome, hyperparathyroidism, and diabetes mellitus, may occur. Some patients may have a progressive diffuse facial deformity called leontiasis ossea; however, this facies may be caused by other disorders as well, including Paget's disease and craniometaphyseal dysplasia. Malignant transformation to sarcoma occurs in about 0.5 percent of patients with fibrous dysplasia and 4 percent of those with the McCune-Albright syndrome. This tumor is rare in the skull.

Differential Diagnosis. Fibrous dysplasia must be differentiated from benign and malignant neoplasms, including meningioma with adjacent hyperostosis, sarcomas or fibromas replacing bone, bone cysts, and various orbital masses, including eosinophilic granuloma, Hand-Schuller- Christian disease, and orbital pseudotumor. , In addition, other metabolic diseases of bone must be considered, including Paget's disease, hyperparathyroidism, hyperostosis frontalis interna, osteopetrosis, and craniometaphyseal dysplasia (Pyle's disease). In general, age of onset, other clinical features, and radiological features easily distinguish these disorders. Rarely, the cranial hyperostosis found in hematological disorders causing bone marrow hyperplasia or cyanotic heart disease may cause confusion.

Evaluation. Evaluation should seek to distinguish fibrous dysplasia from other tumors or metabolic diseases and to assess the presence of deficits that require follow- up or surgical intervention. Plain x-ray films, CT, and MRI can distinguish fibrous dysplasia from tumors and characterize other metabolic disorders. Meningioma with adjacent hyperostosis is distinguishable on CT and MRI by its typical enhancement and its extension into the cranial cavity. Fibrous dysplasia expands into the outer table, leaving the inner table and cranial contents undisturbed. Imaging dedicated to the optic foramina should be done when the frontal and sphenoid bones are involved. Skeletal survey and increased uptake on bone scintiscanning can identify asymptomatic areas of involvement. Serum alkaline phosphatase levels are often elevated, but serum calcium and inorganic phosphorus are normal, helping to differentiate hyperparathyroidism. When following patients with frontal and sphenoid involvement who have not had surgery, photographs of the head, quantitation of proptosis, documentation of acuity and visual fields, and funduscopic examinations for optic atrophy should be performed along with radiological views of the optic canal. These parameters may then be followed every 3 to 6 months until it is clearly established that no progressive visual loss has occurred. The onset of pain, increasing alkaline phosphatase levels, rapid growth, or invasion into cortical bone should raise a suspicion of possible malignant transformation. Biopsy may be needed to distinguish progression of fibrous dysplasia from malignant transformation.

Management. Treatment is indicated when clinical function is significantly threatened. When visual symptoms are present in patients with a small or diminishing optic canal, surgical decompression by unroofing the optic canal can in most cases arrest progression. Such treatment rarely leads to significant return of function; therefore, patients at risk for visual loss must be closely followed. The lesions are highly vascular, and intraoperative bleeding and intrabony hematomas may complicate surgery. Radiotherapy is contraindicated because it greatly increases the risk of malignant transformation. Because lesions may progress more rapidly during pregnancy, careful follow-up, especially for visual symptoms, must be maintained. Decisions about surgery during pregnancy should be based on the neurological status of the patient.

Prognosis and Future Perspectives. The course in most cases is benign. Leeds and colleagues followed 15 patients for 6 to 39 years and found that radiological progression was slight or equivocal in all except two patients. Yet although the lesions become less active after skeletal maturation, progression does not necessarily stop with bone growth, and the lesions may reactivate during maturity. Recent success in elaborating the molecular mechanisms of intracellular signaling and their alterations in fibrous dysplasia and other diseases opens a rich field in which our understanding of the pathogenesis of fibrous dysplasia can be deepened. The elaboration of this work is likely to clarify the endocrinological manifestations of fibrous dysplasia. A better understanding of the molecular pathogenesis may eventually produce effective therapies, as it has in Paget's disease of bone.

Paget's Disease

Pathogenesis and Pathophysiology. Paget's disease (osteitis deformans) is a metabolic bone disease of un known etiology characterized by increased osteoclast size and activity that results in resorption of bone followed by reactive new bone formation. This process produces areas of bone resorption with new bone laid down in an abnormally dense mosaic pattern. The osteoclasts in affected bone contain nuclear and cytoplasmic virus-like inclusions, and evidence has been presented of an association with various paramyxoviruses, including measles virus, respiratory syncytial virus, and canine distemper virus. It has been speculated that the disorder represents the late effect of viral infection on osteoclasts or their precursors and that affected osteoclasts tend to form multinucleated syncytia, which have increased resorptive activity. Normal osteoblasts may then be stimulated by the primary pathological osteolytic disorder.

Epidemiology and Risk Factors. Paget's disease is the second most common metabolic bone disease in the elderly population, after osteoporosis. It is most common in patients of northern European ancestry and is uncommon among Asians and Africans. Males predominate slightly. The prevalence in the elderly population of the United States is 1 to 3 percent, with 0.1 to 0.2 percent of patients having significant symptoms. The risk is increased in relatives of those affected, but pedigrees do not support direct inheritance.

Clinical Features and Associated Disorders. The disease typically begins in middle age or later and varies from limited asymptomatic involvement of a single or few sites to widespread symptomatic disease. The femur, pelvis, and spine are most commonly affected, although any bone may be involved. Skull involvement is also common. The most typical presenting symptoms are focal progressive bone pain, deformity due to expansion of bone, and structural failure such as vertebral compression fracture or bowing of weight-bearing long bones. Enlarging hat size due to progressive skull expansion is a classic symptom. Other typical facial changes include enlarged and coarsened orbits and prognathism. Patients may also notice focal increases in skin temperature due to increased blood flow at affected sites. The most common neurological symptoms are headache, deafness, and problems resulting from spinal disease. The cause of the deafness is unclear. Both auditory nerve compression and involvement of the middle ear ossicles have been suggested as mechanisms; however, autopsy studies have not borne out either hypothesis. , The main mechanisms presumed to cause neurological symptoms are compression of neural and vascular structures by overgrowth of bone into limited spaces, traction on neural structures displaced by bony deformity, and possibly a vascular steal phenomenon resulting from the local high blood flow demand of pagetic bone ( Table 29-4 ). Involvement of the skull may cause basilar impression with consequent problems, including headache, ataxia, hydrocephalus, myelopathy, or cranial neuropathies. Patients may develop intradiscal lesions with spinal stenosis and, rarely, extramedullary hematopoiesis. These lesions may cause back pain or may progress to cause spinal cord and nerve root compression. Yet compressive symptoms due to spinal disease are uncommon, and when they occur in patients with Paget's disease, the possibility of sarcomatous degeneration should be considered. High-output heart failure due to the highly vascular shunts is rare.

 

TABLE 29-4 -- NEUROLOGICAL COMPLICATIONS OF PAGET'S DISEASE

Deficit/Localization

Proposed Mechanisms of Injury

Hearing loss

 

Conductive

Involvement of middle ear ossicles

Sensorineural

Compression/traction of auditory nerve

Spinal cord and root involvement

Compression of central canal and foramina

Radiculopathy (esp. lumbosaeral)

Compression, traction

Myelopathy (esp. thoracie)

Compression, vascular compromise (?steal)

Cranial nerves and brain stem

 

Olfactory nerve

Sphenoid thickening compromising lamina cribosa

Optic nerve

Optic canal stenosis, orbital compression, ?vascular steal

Oculomotor nerves

Superior orbital fissure stenosis, ?vascular steal

Trigeminal nerve

Foraminal compression, ?vascular steal

Facial nerve

Facial canal stenosis, ?vascular steal

Lower cranial nerve, brain stem, cerebellum

Foraminal stenosis, basilar impression, platybasia, and vertebral artery compression from compression within foramina tranversaria

Major categories are listed in order of decreasing relative frequency. Among cranial nerve deficits, those of the lower cranial nerves are most common.

 

From 1 to 5.5 percent of patients with Paget's disease develop osteogenic sarcoma. Other tumors, such as giant cell tumor of bone, are less common. The pagetic osteogenic sarcoma is osteolytic, and pathologic fracture is the most common presentation. Malignant degeneration should also be suspected when a rapid increase in pain or growth is noted or when compressive spinal findings emerge. About 5 percent of patients have hyperparathyroidism, but the mechanism of this association is not known. A complex array of vitamin D-related disorders may also accompany Paget's disease.

Differential Diagnosis and Evaluation. The differential diagnosis includes primary and metastatic bony tumors, especially prostate cancer, and other metabolic bone disorders that produce lytic lesions and hyperostosis. Degenerative arthritis may cause confusion, especially when one is trying to determine the source of symptoms when the two diseases coexist.

Plain radiographs of affected bones are still the primary means of diagnosis. The bones are expanded, often with thickening of the cortex. There may be a peripheral edge of lytic fronts and a small intracortical lytic area. It is common to find lytic lesions predominating in the skull. The most striking feature is typically osteosclerosis, which may have a fluffy appearance. The sclerosis is often intermixed with lytic disease. Uniformly sclerotic ivory vertebrae may be seen. Radionuclide scanning demonstrates greatly increased uptake and is the most sensitive test to establish the extent of involvement. Computed tomography can be used to distinguish osteolytic lesions missed on plain radiographs and can identify soft tissue masses . In this regard, it may be an important adjunct in the differentiation of benign lesions from tumor. The urinary hydroxyproline-creatinine ratio is elevated, reflecting increased bone resorption. Greatly elevated bone alkaline phosphatase levels reflect increased osteoblastic activity and are characteristic. The relative elevations of these values reflect the predominance of either lytic (early) or blastic (late) disease. Serum calcium is usually normal unless some other factor, such as immobilization, tips the balance in favor of resorption and hypercalcemia. Inorganic phosphorus is normal or slightly elevated. When malignant degeneration is suspected, as in a patient with a pathological fracture, early biopsy should be pursued.

Management. The management of Paget's disease has changed in recent years. Both bisphosphonate and calcitonin attack the underlying metabolic disorder by inhibiting bone resorption. Although there is no consensus on the best therapy, both are now being applied to prevent the development of long-term complications. Etidronate, the first bisphosphonate available, provides definite benefit by inhibiting osteoclast activity. However, it interferes with the normal mineralization of new bone. The newer bisphosphonates, such as pamidronate, are similarly effective without impairing mineralization. These agents may be given in short courses intravenously or chronically by mouth. The urinary hydroxyproline level begins to fall within days of an intravenous dose, and the serum alkaline phosphatase declines later and more gradually. These substances remain in bone for a long time and may promote prolonged remissions. Subcutaneous or nasally administered calcitonins also inhibit osteoclasts. Symptomatic relief follows; however, the effect is short-lived, and the agents must be continued to maintain this effect. A loss of effect during therapy may be due to the formation of neutralizing antibodies, which occurs in about one fourth of those treated. The cytotoxic plicamycin used for hypercalcemia of malignancy causes a rapid improvement but is more toxic than the bisphosphonates or calcitonins. Gallium nitrate has antiosteoclastic activity, but data on its clinical use do not yet support its use outside of controlled trials. The goals of treatment are to normalize metabolism as evidenced by biochemical markers and to relieve symptoms. Most patients obtain relief from bone pain. Reversal of neurological deficits and stabilization--and rarely improvement--of hearing often follows therapy. There has been radiological evidence of healing of osteolytic lesions. Malignant lesions should be treated aggressively with radical resection for best results. Chemotherapy has not yet been shown to be effective. Early detection is currently the only available way to improve survival. Patients require life-long surveillance for tumor recurrence. With the currently available array of effective therapies for Paget's disease, it is most important that patients be properly referred for expert care.

Prognosis and Future Perspectives. Many patients remain asymptomatic. Newer drug therapies can now address bone pain and other rarer symptoms and may offer long-term remission. However, as noted previously, prevention or early detection of neurological deficits is essential to avoid loss of function, since therapy is more likely to arrest than to reverse them. The prognosis after malignant degeneration has occurred, however, remains poor, with only about 10 percent of patients surviving 5 years. Research in Paget's disease has produced advances in the understanding of the possible underlying etiology, the metabolic processes that promote the disorder, and the application of several new therapies. Further clarification of the viral hypothesis, development of improved diagnostic metabolic markers, and refinement of management with antiosteoclastic agents are expected in the future.

Other Compressive Disorders

Numerous other less common structural disorders are occasionally associated with compressive neurological signs and symptoms, including hyperostosis frontalis interna, anomalies of the craniocervical junction, congenital and acquired abnormalities of the spinal cord, generalized skeletal abnormalities, and such miscellaneous disorders as arachnoid diverticula. The clinical signs and symptoms of these disorders are summarized in Table 29-5.

Compressive Neuropathies

COMPRESSIVE DISORDERS OF THE MEDIAN NERVE

Pathogenesis and Pathophysiology. The median nerve is subject to compression at the wrist, where it accompanies the flexor tendons as they pass beneath the volar carpal ligament. This region, the carpal tunnel, is a closed space within which pressure may rise. Studies with recording wicks placed in the canal show that flexion or extension elevate the canal pressure and that thickening of tendon sheaths or encroachment by other structures leads to a sustained rise in pressure within the canal. Compression of the median nerve at the wrist then leads to the carpal tunnel syndrome (CTS), the most common of the

 

TABLE 29-5 -- OTHER STRUCTURAL DISORDERS AND ASSOCIATED NEUROLOGICAL SYNDROMES

Disorder

Neurological Syndrome

Hyperostosis frontalis interna

Headache

Anomalies of the craniocervical junetion region

 

Basilar impression

Brain stem, cerebellar, and cranial nerve compression

Chiari malformations

Brain stem, cerebellar, and cranial nerve compression

Atlantoaxial subluxation (e.g., congenital, rheumatoid arthritis, Down's syndrome)

Cord and lower brain stem compression

Congenital and acquired abnormalities of the spinal cord

 

Klippel-Feil syndrome

Cord and root compression

Scoliosis

Cord and root compression

Kyphosis

Cord and root compression

Generalized skeletal abnormalities

 

Achondroplasia

Spinal stenosis, disc disease, basilar impression

Mucopolysaccharidoses

Cord and root compression, basilar impression

Down's syndrome

Atlantoaxial subluxation, basilar impression

Osteoporosis

Cord and root compression

Osteoporosis

Brain stem and cord compression

Osteomalacia

Cord and root compression, basilar impression

Osteitis fibrosa cystica (hyperparathyroidism)

Basilar impression

Osteogenesis imperfecta

Basilar impression

Miscellaneous disorders

 

Arachnoid diverticula

Cord and root compression


entrapment neuropathies.
Although nonspecific tenosynovitis is the most common cause of rising canal pressure, other causes may be relevant: amyloidosis may infiltrate the tendon sheaths, rheumatoid arthritis may cause synovial tissue to invade the canal, or hypothyroidism may cause tissue edema.

The median nerve is subject to compression at proximal sites near the elbow by a hypertrophied pronator teres muscle, by a vascular anomaly, or by trauma .The symptoms and signs of proximal median neuropathy differ from those of CTS because the entire median nerve, including the motor branches to the flexors of fingers and thumb, is affected.

The archetypal motor and sensory loss anticipated with a lesion of the median nerve at three different levels is summarizedin Table 29-6 . Not all listed muscles are always affected, and EMG testing is more sensitive than manual muscle testing.

Epidemiology and Risk Factors. The degree to which CTS is an occupational disorder is still disputed. Reported work- and trauma-related disorders of the upper extremities have increased tenfold in the past two decades, although only a small proportion relate to CTS. There is no consistent agreement about the diagnostic criteria, particularly whether the diagnosis requires confirmation by nerve conduction velocity (NCV) testing. In a Mayo Clinic retrospective chart review, using both NCV and clinical criteria, the prevalence of CTS was 125 per 100,000.

It is estimated, based only on clinical criteria, that half of the cases of CTS seen in the United States are work- related. Motions of the wrist that require frequent rotation or flexion-extension, especially with force, seem to produce the highest incidence of disease. Carpenters, butchers, office workers who use keyboards, dental assistants, and musicians have a high incidence of CTS. Many workplaces have made ergonomic redesign a priority because of the rising medical costs of overuse syndromes, including CTS. Other overuse syndromes include tendinitis, tenosynovitis, local arthritis, vasospastic conditions due to vibration, and functional thoracic outlet syndrome. The last of these is discussed subsequently.

Symptoms of CTS are common in the latter months of pregnancy, probably because of rising tissue pressures due to fluid retention. In the majority of instances, the symptoms

TABLE 29-6 -- MEDIAN NERVE COMPRESSION

Location

Muscles Affected

Action

Sensory Loss

At the wrist

Abductor pollicis

Abduction

Palmar and dorsal surfaces of thumb, index, middle fingers

Opponens pollicis

Opposition

Near elbow (pronator syndrome)

Abductor pollicis

Abduction

Palm, palmar and dorsal surfaces of thumb, index, middle fingers (no loss on forearm)

Opponens pollicis

Opposition

Pronator quadratus

Pronation

Pronator teres

Pronation

Flexor pollicis longus

Flex thumb, distal joints

Flexor digitorum sublimis

Flex fingers

Flexor digitorum profundus

Flex fingers, median side

Flexor carpi ulnaris

Wrist flexion

Lumbricals

Extend MP joint

Below elbow

Flexor pollicis longus

Flex thumb, distal joint

None

Flexor digitorum profundus II

Flex index finger, distal joint

 

promptly resolve with delivery. Women are more likely to be diagnosed with CTS than men by a ratio of 60:40. In patients with occupational CTS, this ratio may be reversed. The higher frequency in women may reflect smaller wrist circumference, which correlates with CTS in some studies, or the different work conditions experienced by women.

Clinical Features and Associated Disorders. Patients with classic CTS report nocturnal distal pain and paresthesias. Pain may be present throughout the arm up to the level of the shoulder, but tingling is typically felt more distally. Some patients can detect the location of the tingling in the index and middle fingers, but many find it more difficult. Typically, patients rub and shake the hand because it feels asleep. On examination, patients in the early stages of disease have slight weakness of thumb abduction (away from the plane of the palm) and slight sensory loss, which is sometimes best detected on the dorsum of the index and middle fingers. There may be paresthesias into the palm with tapping over the wrist crease (Tinel's sign) and with forced wrist flexion for 30 seconds (Phalen's sign). In the later stages, patients have visible thenar atrophy and marked weakness of thumb abduction and opposition. Atypical forms of CTS exist, and one may observe marked autonomic dysfunction, acute onset, marked sensory loss, or unexpected neurological findings due to anatomical variations.

Patients with proximal median neuropathy may have partial or confusing deficits. Often the diagnosis is suspected because deep palpation over the course of the median nerve is painful and causes paresthesias.

In about 75 percent of patients, CTS is accompanied by nonspecific tendinitis in the flexor tendons. Hypothyroidism, atypical mycobacterial infection, diabetes, rheumatoid arthritis, and acromegaly are also associated with CTS. Pregnancy accounts for about 1 percent of CTS cases. In half the patients with symptomatically unilateral CTS, NCV in the opposite extremity is delayed. Additional ulnar nerve compression, cervical radiculopathy, bursitis, tendinitis, and osteoarthritis often occur in CTS patients, as well as an array of rheumatological complaints.

Differential Diagnosis. Cervical radiculopathy is a common diagnostic issue when the diagnosis of CTS is under consideration. Patients with radiculopathy are more likely to report neck pain, radiating pain with coughing or sneezing, and daytime (as opposed to nocturnal) paresthesias. With C6 or C7 radiculopathy, the biceps or triceps tendon reflex may disappear. Sensory loss proximal to the wrist is not characteristic of median neuropathy. A theory that proximal compression of a nerve root will worsen distal entrapment by impairing axonal transport (the so-called double-crush syndrome) has not been proved. Most investigators believe that in patients with two sites of compression, for instance, C6 radiculopathy plus CTS, the disabilities are purely additive.

Large vessel vascular disease, leading to hemispheric transient ischemic attacks (TIAs), must be considered because the paresthesias of CTS may be brief enough to suggest TIAs. However, TIAs are rarely nocturnal and are not painful or unpleasant. Furthermore, hand tingling in a person with a TIA is usually associated with other neurological signs.

Diffuse peripheral neuropathy is a diagnostic problem with respect to CTS; it may complicate the electrophysiological investigation. Diabetic axonal neuropathy is the commonest coexisting neuropathy.

Evaluation. A diagnosis of CTS is usually evident from the history, and the neurological examination should focus on excluding other possible diagnoses. Tinel's and Phalen's signs are present in about half of patients with CTS and may be helpful. Electrophysiologic testing is important for the diagnosis of CTS and should be carried out in nearly every instance prior to surgical release. If the clinical picture is straightforward and no therapy is planned other than conservative measures, electrophysiological testing can be omitted. Testing depends on the measurement of sensory action potentials from median innervated digits, especially the index finger, and comparison with other sensory potentials in that hand, such as radial or ulnar. Comparison with the opposite hand is usually done, but the results are limited by the high frequency of bilateral nerve conduction abnormalities. In a typical patient with mild CTS, the size of the median sensory action potential is maintained, but demyelination causes delay when it is measured at the wrist. In more advanced cases the compound muscle action potential is also delayed.When the findings are not clear-cut, other comparisons can be made, and sequential recordings over the nerve as it passes through the palm can demonstrate the actual site of sensory delay when that is necessary. EMG recordings from abductor pollicis brevis and comparison with other intrinsic hand muscles can be made to be certain that only the muscles innervated by the median nerve are affected; this is especially helpful when cervical root disease is being considered. There are numerous pitfalls provided by anatomic variations, such as the Martin-Gruber anastomosis, in which nerve fibers destined to innervate the thenar muscles are found in the median nerve at the elbow but join the ulnar nerve in the forearm and pass the wrist in the ulnar nerve, giving the electrophysiological appearance of a marked loss of motor potential with stimulation of the median at the wrist. When median neuropathy near the elbow is being considered, the EMG pattern is most helpful because nerve conduction tests show diagnostic changes in no more than a third of cases.

Management. Many patients with CTS are managed successfully by conservative means, with reduction of any activity that may exacerbate tenosynovitis, use of a wrist splint, and oral nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen 1600 mg/day or naproxen 750 mg/day. The splint should hold the wrist in a few degrees of extension and may be worn at night or during wrist use. Prolonged or continued wrist splint use may lead to reduced range of motion and should be discouraged.

Steroid injection within the carpal canal is a time-honored technique and may be helpful diagnostically. After local anesthesia of skin and subcutaneous tissue, 15 to 30 mg of a depot preparation of methyl prednisolone is injected. The needle should be introduced 2 to 3 cm proximal to the palm itself and to the ulnar side of the palmaris longus tendon; injection into the nerve is to be avoided. No more than three injections should be done, since damage to the tendons may occur with frequent use of local steroids. Injection may provide relief of symptoms for several months, but symptoms recur in over 80 percent of patients. Injection is particularly suitable for pregnancy-related CTS.

Patients who have persistent symptoms following conservative management should be referred for surgical release, and those with sensory or motor deficits normally require surgery. Advanced disease, especially in the elderly, will not improve motorically, so the only reason for surgery is to provide relief from pain. The degree of slowing of NCV is not a good predictor either of the need for surgery nor for outcome. The results of surgery are generally excellent. Forty percent of patients are asymptomatic following surgery, and another 40 percent have only trivial residual symptoms. Long-lasting incisional pain, slight weakness of the wrist, and a small number of patients who are neurologically worse after surgery are found in 10 percent of surgical outcome studies.

Prognosis and Future Perspectives. In general, the prognosis for CTS is good. The condition is not disabling unless there are compounding problems such as compensation issues, psychological impairment, reflex sympathetic dystrophy, or an occupation requiring great strength or precise control of the digits (as in instrumental musicians).

Surgical techniques are under constant review and modification. Several procedures for endoscopic carpal tunnel release have been introduced. Overall, these seem to have efficacy that is about equal to that achieved with standard release procedures, as judged by randomized trials reported thus far. There have been reports of hemorrhage within the palm, ulnar nerve compromise, and other complications that do not occur with standard release. The endoscopic procedure needs further evaluation.

In many industries, major efforts have been made to avoid the risk of occupational CTS, along with other overuse syndromes, by undertaking ergonomic redesign of work stations and tools. These efforts will continue in the future, since the economic consequences of these conditions can be very severe. In fact, within the last 2 years, premiums for worker compensation insurance have fallen slightly in many parts of the United States, possibly signaling a change in incidence of overuse and CTS in the workplace.

COMPRESSIVE DISORDERS OF THE ULNAR NERVE

Pathogenesis and Pathophysiology. The ulnar nerve is subject to entrapment at the elbow and, less commonly, can be traumatized in the palm or at the wrist. The common site of compression is at the cubital tunnel, which consists of the edge of aponeurosis of the flexor muscles, beneath which the nerve must pass . This area is located about 3 to 5 cm distal to the medial epicondyle. Compression within the cubital tunnel is increased by elbow flexion. Less commonly, the nerve can be compressed externally at the elbow groove (for instance, during anesthesia), or by synovium in rheumatoid arthritis patients, or by callus following a fracture.

Epidemiology and Risk Factors. The prevalence of ulnar nerve disorders is unknown. Based on the apparent frequency of abnormalities in routine EMG/NCV studies, asymptomatic or minimally symptomatic ulnar neuropathy is very common, approaching the range of incidence of CTS.

Risk factors for ulnar neuropathy are poorly defined. Arthritis of the elbow may be a contributing cause. Persons who habitually rest the flexed elbow on a table or chair, specifically those with chronic pulmonary disease, can compress the nerve. There is a much lower incidence of ulnar neuropathy as an occupational disorder compared with CTS, but musicians who use one arm in a flexed position (cellists, violinists) commonly develop ulnar neuropathy. In baseball pitchers, particularly those who employ the slider and curve ball pitch are more at risk than fast ball pitchers. Other than these exposures, ulnar neuropathy is more common in the nondominant side, suggesting that repeated elbow flexion is more important etiologically than is repeated muscular usage. Ulnar neuropathy at the elbow is the most common anesthesia-related compressive neuropathy.

Ulnar neuropathy at the wrist can be caused by ulnar artery thrombosis at that site, by lacerations or ganglia. The ulnar nerve lies outside the carpal tunnel adjacent to the ulnar artery. The first occupational focal neuropathy described was observed by Ramsay Hunt, who reported compression of the ulnar nerve at the wrist in telegraph operators, who used the proximal palm to tap the key.

Clinical Features and Associated Disorders. The first symptoms in the majority of patients with cubital tunnel syndrome involve intermittent hypesthesia in the ulnar distribution. This is often associated with elbow flexion and dissipates with elbow extension. These symptoms may vary during the day and from day to day, disappearing for a period of time. Pain around the elbow, tenderness over the cubital tunnel, or radiating pain traveling into the palm may also be present. The amount of pain and paresthesia vary, and for some individuals the sensory loss is not bothersome. Although most patients present with sensory complaints, motor dysfunction, including weakness of intrinsic hand muscles and decreased grasp or pinch, or a loss of dexterity, can occur. An early motor symptom can include a loss of control of the fifth digit due to weakness of the third palmar interosseous muscle. In other patients, no early symptoms are noted, and the patient eventually presents with marked muscular atrophy and weakness. (See Table 29-7 for individual muscles and sensory distribution.)

Diabetes mellitus may be a comorbid illness and seems to predispose to ulnar neuropathy, possibly by impairing the microvasculature of the nerve. Rheumatoid arthritis may cause synovial overgrowth and compress the ulnar nerve.

Differential Diagnosis. Neurogenic thoracic outlet syndrome, due to an aberrant ligament or band compressing the inferior trunk of the brachial plexus, is described later. The clinical findings may resemble those of ulnar neuropathy. This entity can be detected by finding weakness in median innervated muscles as well as ulnar innervated muscles and by the presence of sensory loss on the medial forearm. The same anatomical features pertain to metastases or a primary tumor within the brachial plexus or to radiation plexopathy. Cervical spondylosis affecting the C8 nerve root is quite rare; most radiculopathies affect the C6 or C7 root. Symptomatic thoracic outlet syndrome, in which the plexus is compressed by elevated arm positions or by muscular spasm, does not cause sustained neurological abnormalities.

Evaluation. The sensory examination is important, particularly in cases of early disease, in which sensory abnormalities may be the only findings. Sensory loss with ulnar neuropathy typically stops at the wrist creases. If the ulnar neuropathy is at the level of the wrist, the dorsum of the hand will be spared. Clinical evaluation should include a careful study of the pattern of weakness. Ulnar neuropathy causes weakness of adduction and abduction of all fingers, and adduction of the thumb. Importantly, flexion of the terminal phalanx of the fifth (or fourth and fifth) digit is carried out by the flexor digitorum profundus IV and V, a muscle that is located in the forearm. If this is the only flexor found weak, cubital tunnel syndrome is very likely.

With lesions of the ulnar nerve above and at the elbow, there can be atrophy and flattening of the hypothenar eminence and interossei. The hand may demonstrate a "claw-hand" deformity (main en griffe), with the fifth, fourth, and, to a lesser degree, the third fingers hyperextended at the metacarpophalangeal joints and flexed at the interphalangeal joints. The hyperextension at the metacarpophalangeal joints results from paralysis of the interossei and ulnar lumbricals. This results in the unopposed action of the long finger extensors; the flexion at the interphalangeal joints is due to tension from the long finger tendons. Ulnar paresis or paralysis also affects extension at the interphalangeal joints of the second to fifth fingers, adduction and abduction of the second to fifth fingers, and abduction and opposition of the fifth finger. Froment's prehensile thumb sign (signe du journal) may be present as a result of adductor pollicis weakness. This sign occurs when a sheet of paper, grasped between the thumb and index finger, is pulled; the proximal phalanx of the thumb is extended, and the distal phalanx is flexed.

Electrophysiological testing focuses on the demonstration of slowing of motor and sensory fibers at the elbow. Sometimes it is possible to show that only the ulnar nerve is affected but not to localize the disorder well. This happens particularly when there is significant axonal loss in patients with long-standing neuropathies.

Management. Conservative management consists of reducing occupational exposure, if any, using NSAIDs, and using a half-splint held in place with a wrap, so that the elbow is maintained in gentle extension. Such a splint can be worn at night as well as during the day. Steroid injections

 

TABLE 29-7 -- ULNAR NERVE COMPRESSION

Location

Muscles Affected

Action

Sensory Loss

At elbow (cubital tunnel syndrome)

Flexor digitorum profundus V

Flexes little finger, distal joint

Medial side of hand and fingers to wrist crease

Interossei

Adducts and abducts

Flexor pollicis brevis

Adducts thumbs

Opponens V

Adducts little finger

At wrist

Interossei

Adducts and abducts

Palmar and medial hand and finger

Flexor pollicis brevis

Adducts thumb

Opponens V

Adducts little finger


have no role in the treatment of patients with the cubital tunnel syndrome.

The decision to refer patients for surgery should be based chiefly on the presence of a demonstrated worsening deficit, even if mild. Many ulnar neuropathies stabilize and remain mild. Pain may be a significant problem and may force an early decision for surgery. The choice of a procedure is not without controversy. Many surgeons prefer a simple cubital tunnel release, by sectioning the taut aponeurosis. Others remove the medial epicondyle, which forms the medial wall of the ulnar groove, in order to decompress the nerve. Mobilization of the nerve and moving it to a position above the epicondyle and beneath the flexor muscles produces a definitive decompression. Attention to arm position during anesthesia will help to cut down on perioperative neuropathy. In many patients the condition stabilizes at a mild or moderate degree of nerve dysfunction.

COMPRESSIVE DISORDERS OF THE RADIAL NERVE

The radial nerve is subject to compression at several sites ( Table 29-8 ). An acute compression can occur at distal parts of the brachial plexus, in which the nerve is compressed against the humerus, usually when the patient falls asleep with the arm draped over a chair; this is the so-called Saturday night palsy. Fractures involving the shaft of the humerus can damage the nerve, since it is closely applied to the bone through much of its course. There is a radial tunnel located beneath the extensor carpi radialis, 3 to 4 cm distal to the lateral epicondyle. Finally, the radial sensory branch, supplying the dorsum of the wrist and hand, is subject to laceration or contusion .

Persons subject to acute intoxication from alcohol or drugs are those most likely to develop an acute radial nerve compression. The radial tunnel syndrome is usually chronic and is associated with anatomical variations near the elbow that have no predictable risk factors.

Radial nerve palsy causes wrist drop with paralysis of finger and thumb extension. Because the intrinsic hand muscles are weak in this position, apparent palsy of finger abduction is seen; this can be corrected by supporting the fingers. In patients with acute Saturday night palsy, the brachioradialis is weak, but the triceps muscle is usually only partially affected. Sensory loss is usually slight. The radial tunnel syndrome affects the posterior interosseous nerve, so that wrist extension can be spared because the extensor carpi radialis is above the level of the compression. Local pain and a Tinel's sign at the site of the radial tunnel help to identify this uncommon syndrome.

Radial tunnel syndrome can resemble the signs of a C7 radiculopathy, but the weakness of the finger flexor muscles seen with the C7 deficit soon leads to correct localization. Acute radial palsy is usually painless, but the pattern of weakness, including pseudo-weakness of intrinsics, is readily recognizable. Focal motor neuropathy, which is probably a variant of chronic inflammatory neuropathy, often affects the radial nerve at the region of the elbow; usually other nerves are affected too. Radiological studies are usually not required. If there is a question of hematoma or fracture, plain films or ultrasound examination will suffice.

 

TABLE 29-8 -- RADIAL NERVE COMPRESSION

Location

Muscles Affected

Action

Sensory Loss

At elbow (posterior interosseus syndrome)

Extensor carpi ulnaris

Extends wrist

None

Extensor digitorum communis

Extends fingers

Extensor pollicis

Extends thumb

Abductor pollicis

Extends, abducts

Below elbow (sensory radial branch)

None

 

Lateral side of forearm and hand


If nerve conduction studies are carried out acutely, they will show conduction block because the acute disorders are demyelinative in most instances. Electromyographical studies in patients with radial tunnel syndrome can be very helpful in locating the exact site of nerve compression.

If an acute radial palsy lasts for more than a few days, the patient should be referred for physiotherapy and for occupational therapy to allow fitting of a spring-loaded brace for finger and wrist extension. Radial tunnel syndrome patients may require surgical exploration; the two indications for surgery are pain and established or progressing weakness. Acute radial palsy patients usually recover completely within 4 to 6 weeks. Even after severe injury to the nerve, full late recovery can occur. With bracing, acceptable use of the hand can be maintained.

THORACIC OUTLET SYNDROME

True neurogenic thoracic outlet syndrome (TOS) is due to an aberrant band or ligament crossing the brachial plexus, usually between the transverse process of the C7 vertebra and the sternum or first or second rib. The inferior trunk of the plexus, consisting of fibers derived from C8 and T1 nerve roots, is compressed. The syndrome is very rare. Symptomatic, or secondary, TOS does not involve an identifiable anatomical structure causing nerve compression and is believed to be due to an abnormal shoulder posture or to muscle spasm. It is most often diagnosed with certainty in persons who use one or both arms above the head or in instrumental musicians. Sometimes there is a preceding history of minor cervical or shoulder trauma precipitating muscle spasm or a change in shoulder or neck posture. Some patients are tall, slender, and more round- shouldered than average ("droopy shoulder syndrome"). In addition, vascular types of compression can occur within the thoracic outlet, usually affecting the subclavian artery. Surprisingly, neurogenic and vascular compression do not usually coexist, most patients demonstrating one pattern or the other, but not both. There are no known risk factors for vascular TOS. Since some patients develop thrombosis of the subclavian or innominate artery, a thrombotic disorder would be a risk factor.

The diagnosis of true neurogenic TOS requires an anatomical abnormality, which is presumably congenital. Symptomatic TOS may be occupational. There may be an overlap with overuse syndrome or with other nerve entrapments, and if the clinical findings are slight, a firm diagnosis may not be possible. True neurogenic TOS causes a stereotyped clinical picture. Patients complain of numbness and pain in the affected arm. There is weakness of all intrinsic muscles of the hand, corresponding to the C8 and T1 myotomes, and often starting with the thenar muscles. Sensory loss, if present, is located on the ulnar side of the hand and forearm. With further compression of the plexus, extensors of the thumb and index finger and pronator quadratus are affected.

Symptomatic TOS causes positional numbness and pain without demonstrable neurological deficit. There may be pain on palpation over muscles or nerve trunks. The radial pulse may diminish with arm abduction, but the value of this observation is much reduced by the fact that it is present in 15 percent of normals.

Alternative diagnoses center around other conditions that affect the lower plexus. These include metastatic cancer, radiation injury, syringomyelia, and, rarely, lower cervical disc herniations. Nerve conduction testing is important, mainly to exclude atypical median or ulnar neuropathies. The plexus injury in true neurogenic TOS is axonal in type, so that reductions in ulnar sensory action potentials, accompanied by EMG findings in the C8 and T1 myotomes, are to be expected. An MRI scan of the plexus and cervical spine is advisable to exclude tumor. Many tests of pulse volume in various arm positions have been described in the past, but they have little role in modern medicine. If there is a suspicion of subclavian stenosis or occlusion, angiography or MR angiography should be carried out without delay.

Symptomatic TOS is treated by physiotherapy, consisting of a program to strengthen the muscles and improve cervical and periscapular strength and posture. Neurogenic TOS may require surgical release; for proper visualization, a retroclavicular approach is best, although an extensive literature describes transaxillary first rib removal, an unproven procedure that has many described complications. The prognosis of patients with symptomatic TOS depends on proper management through physiotherapy. The prognosis of those with neurogenic TOS is unknown owing to the marked rarity of the disorder.

COMPRESSIVE DISORDERS OF THE SCIATIC, PERONEAL, AND TIBIAL NERVES

The sciatic nerve and its branches are resistant to entrapment, and there is no consistent area in the lower extremity where entrapment occurs. Compression of the sciatic nerve can occur in situations in which there is variation in the course of the sciatic nerve between parts of the piriformis muscle, or by a myofascial band in the distal portion of the thigh between the biceps femoris and the abductor magnus. The sciatic nerve can be acutely compressed or injured by retroperitoneal bleeding in the setting of anticoagulant therapy. Surgical trauma from hip replacement, gunshot wounds, fractures of the hip or femur, and infarction are some of the causes of sciatic nerve lesions. Such compression may occur following fractures or other acute traumatic lesions. Forcible inversion of the foot, which results in stretching of the nerve and damage at the level of the fibular head, may cause peroneal dysfunction. Other causes of peroneal damage include improperly applied casts or tight garters, bandages, or stockings. Some patients may be susceptible to peroneal compression including those who were unconscious from drugs, anesthesia, or illness with coma. Excessive weight loss in the presence of chronic illness may also predispose the patient to peroneal compression. Certain occupations including those that require prolonged sitting, squatting, or kneeling may provoke peroneal dysfunction. Finally, ganglia or tumors of the nerve or neighboring structures may be associated with compression of the peroneal nerve. Tibial nerve dysfunction resulting from tarsal tunnel syndrome consists of entrapment of the posterior tibial nerve at the level of the medial malleolus. This syndrome is quite rare and usually occurs after ankle fracture or in patients with rheumatoid arthritis. Any or all of these divisions of the posterior tibial nerve may be affected.

The risk factors for peroneal or sciatic mononeuropathy are those associated with any acute compression, namely, local trauma, fracture, or prolonged unconsciousness. Peroneal nerve compression can occur with prolonged squatting and has been seen in vegetable or fruit pickers working in fields.

Diabetes is a risk factor for sciatic or peroneal neuropathy, probably because it contributes to vascular insufficiency and predisposes to nerve infarction or conduction failure if the nerve is compressed.

The sciatic nerve innervates the knee flexors and all the muscles below the knee. Therefore, complete palsy of the sciatic nerve leads to marked instability of the foot and to a severe impairment of gait. A complete palsy of the sciatic nerve is extremely rare and would not be expected from sciatic nerve entrapment. The entire foot except for a small region supplied by the saphenous nerve over the medial malleolus is supplied by the sciatic nerve. With entrapment, pain or paresthesia may radiate into these territories.

Peroneal palsy is usually acute and is the result of external pressure applied to the nerve in its vulnerable fixed position against the fibula. Loss of eversion (if the superficial division is involved) or of dorsiflexion of the toes and ankle (if the deep division), or both, are found. Sensory loss is much more apparent with lesions of the superficial division, and such loss involves the lateral calf, the lateral malleolus, the dorsum of the foot, and the medial three or four toes up to the interphalangeal joint. With lesions of the deep division, the sensory loss is smaller and involves the small area between the first and second toes and the web space and the adjacent portion of the dorsum of the foot. In common acute compressive peroneal lesions, pain is not a typical complaint, and there are few or no sensory symptoms. With entrapment or chronic lesions, patients may experience radiating pain and slowly progressive motor and sensory disturbances.

The primary symptom of tarsal tunnel syndrome is a burning, unpleasant pain in the sole of the foot. This pain may become worse during rest or while sleeping at night. Pain and sensory disturbances over the entire plantar surface of the foot may occur. With involvement of one or two divisions of the posterior tibial nerve, these findings may be restricted to only a portion of the plantar surface.

Lesions of the sciatic nerve must be distinguished from herniated lumbar disc disease. Most patients with sciatic pain due to lumbar disc disease have monoradicular symptoms. Thus, pain radiating to the lateral side of the foot and small toe is associated with S1 lesions; pain radiating to the dorsum of the foot with L5 lesions; and pain radiating to the medial part of the calf with L4 lesions. Marked weakness of both the anterior tibial and gastrocnemius muscles suggests sciatic neuropathy. Other disorders to be considered in the clinical setting of sciatic nerve dysfunction include lumbar spinal stenosis (see earlier discussion) and vascular (diabetic) neuropathy . In patients with progressive sciatic deficits with pain as the initial symptom, intraspinal carcinoma, lymphoma, and myeloma should be included in the differential diagnosis.

L5 radiculopathy may resemble peroneal dysfunction, yet in most patients there is accompanying back pain or sciatic pain. In these cases, weakness of both eversion and inversion and the loss of sensation above the midpoint of the calf of the outer surface, together with the greater weakness of the extensor hallucis than of the anterior tibial muscle, suggest an L5 radiculopathy.

In distinguishing tarsal tunnel syndrome from other disorders, the examiner should consider the varied causes of foot pain. These include plantar fasciitis, stress fractures, bursitis, and trauma to the plantar nerve distal to the tarsal tunnel. Diabetic neuropathy causing burning painful feet may also be difficult to distinguish from bilateral tarsal tunnel syndrome.

Electromyography and NCV testing are very helpful in the diagnosis of disorders of the sciatic nerve and its branches. Focal slowing at the fibular head, implying a demyelinating process, is usually found in patients with acute or chronic peroneal mononeuropathies. Sometimes in those with severe lesions, there is enough axon loss to obscure this important finding. Many sciatic lesions of diverse causes result in marked axon loss, and no demonstrable area of focal slowing will be found even though the lesion is anatomically focal. In these situations, reliance on the pattern of EMG abnormality is still very helpful. Computed tomography or MRI scanning of the lumbar spine, the retroperitoneal space, and the course of the nerve may be needed to establish an exact anatomical diagnosis. Spontaneously arising and progressive mononeuropathy in the lower extremity always presents the possibility of unrecognized tumor.

Management of these lesions depends entirely on their cause. Pain control with sciatic lesions is best achieved by pharmacological means. In patients with peroneal palsy, a fitted brace (ankle foot orthosis AFO ) should be used to protect against ankle joint damage and improve gait unless the muscle paresis is mild. Even in patients with acute lesions, the prognosis of sciatic or peroneal neuropathy is at best, fair. Too often there is extensive axon loss and a resulting lasting deficit.

OTHER COMPRESSIVE DISORDERS OF THE LOWER EXTREMITIES

There are other uncommon compressive neuropathies of the lower extremities including those involving the femoral,

 

TABLE 29-9 -- OTHER NERVES IN THE LOWER EXTREMITY AND ASSOCIATED COMPRESSIVE SYNDROMES

Nerve

Muscles Affected

Reflex Changes

Sensory Loss

Compressive Causes

Etiological and Anatomic Differential Diagnosis

Femoral

Hip flexors

Reduced knee reflex

Anterior thigh, medial ealf

Idiopathic, iatrogenic by surgery, retroperitoneal, hemorrhage, tumor

Infarction trauma radiculopathies

Knee extensors

Lateral femoral cutaneous

None

None

Lateral thigh

Entrapment

 

Saphenous, ilioinguinal and iliohypogastric

None

None

Medial calf, low abdomen

Iatrogenic surgery, scar after surgery

Trauma, infarction

None

None

Obturator

Thigh adductors

None

Medial thigh (smal1 area)

Pelvic tumor, hematoma

Trauma

Interdigital nerve (Morton's neuroma)

 

 

 

Head of fourth metatarsal

Trauma


lateral femoral cutaneous,
saphenous, ilioinguinal-iliohypogastric, and obturator nerves. The clinical syndromes and common causes are reviewed in Table 29-9 .

 

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