Review Article Address correspondence to Dr Jinny O. Tavee, Cleveland Clinic Foundation, Neuromuscular Center, Cleveland, OH 44195, [email protected]. Relationship Disclosure: Dr Tavee has received personal compensation for manuscript preparation from the Cleveland Clinic Foundation and Elsevier. Dr Levin serves as a board member of the American Board of Psychiatry and Neurology and receives royalties from UpToDate, Inc. Unlabeled Use of Products/Investigational Use Disclosure: Drs Tavee and Levin report no disclosures. * 2015, American Academy of Neurology.

Myelopathy Due to Degenerative and Structural Spine Diseases Jinny O. Tavee, MD; Kerry H. Levin, MD, FAAN ABSTRACT Purpose of Review: This article reviews the current evaluation and treatment of patients with myelopathy due to cervical spondylotic disease and other structural disorders of the spine. Recent Findings: In patients with cervical spondylotic myelopathy, symptom duration, severity at baseline, and possibly age have been identified as key prognostic markers of clinical course and postsurgical outcome. Other potential markers include specific MRI and EMG findings. The diagnosis and monitoring of syringomyelia is enhanced by the addition of phase contrast MRI, which evaluates CSF flow dynamics. Flexion MRI is helpful in establishing the diagnosis of Hirayama disease, which is now attributed to a tightened dural sac that is displaced anteriorly on neck flexion, compressing the cord. Summary: Advances in neuroimaging along with new insights into the pathophysiology of structural spine diseases can help guide clinical decision making and optimize patient outcomes. Continuum (Minneap Minn) 2015;21(1):52–66.

INTRODUCTION Degenerative abnormalities related to the aging spine constitute the largest group of disorders that cause spinal cord dysfunction. In particular, cervical spondylotic disease is the most common cause of myelopathy in patients over the age of 55 and accounts for nearly 25% of all hospitalizations for spastic quadriparesis.1,2 Other non-neoplastic structural lesions that may lead to myelopathy include the spondyloarthropathies, syringomyelia, congenital stenosis, and other developmental abnormalities of the spine. CERVICAL SPONDYLOTIC MYELOPATHY Pathophysiology The development of cervical spondylotic myelopathy is due to a combination of factors, which include external compres-

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sion from spondylotic canal stenosis, biomechanical stretch injury, and vascular factors. Spondylosis refers to agerelated degenerative changes of the spine and typically begins with desiccation of the intervertebral disks. Bulging or herniation of disk material follows, resulting in increased mechanical stress and the development of osteophytes along the vertebral endplates.3 Over time, these bony outgrowths combine with degenerated disks to form osteophytic bars that can impinge upon the ventral aspect of the spinal cord. Calcification of the posterior longitudinal ligament may also compress the cord ventrally, while ligamentum flavum pathology (eg, hypertrophy, calcification) may compromise the cord dorsally. Facet joint arthropathy and uncovertebral (joint formed by

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the inferior aspect of the vertebral body and uncinate processes) hypertrophy may further contribute to spinal canal stenosis and cord compression (Figure 3-1). Cervical spondylotic myelopathy may also occur in the setting of congenital spinal canal stenosis, which is defined as a sagittal (anterior-posterior) diameter of less than 13 mm. With the normal adult cord measuring 10 mm in the cervical region, a sagittal diameter of 12 mm or less places the cord at risk for compression, whereas a spinal canal measuring 16 mm or more is considered low risk.4 Stretch injury, which occurs with cervical flexion and extension movements within a narrowed canal, is now thought to play a significant role in the development of myelopathy. Local tethering in conjunction with cord deformation anteriorly, against an osteophytic bar, or posteriorly, against a hypertrophied ligamentum flavum, results in axon and myelin disruption.4 Although these physiologic changes may initially be transient, repetitive injury may ultimately result in permanent neurologic dysfunction.4 Chronic spinal cord ischemia due to compression of the anterior spinal artery and microvasculature is the third major factor (in addition to spondylotic canal stenosis and biomechanical stretch injury) in the pathophysiology of cervical spondylotic myelopathy. This is supported by cadaveric studies demonstrating histologic findings of necrosis and cavitation in gray matter and long tract regions.3,5 Ischemic injury to the cord may also be caused by compression of draining veins and changes in venous dynamics resulting in venous congestion. Other proposed pathophysiologic factors include induction of apoptotic pathways, excitotoxicity, and neuroinflammation.5 Epidemiology Cervical spondylotic changes occur naturally with aging and appear radioContinuum (Minneap Minn) 2015;21(1):52–66

graphically in over 90% of the population aged 65 or older, although most patients are asymptomatic.6 Of those with symptoms, which include neck pain and radiculopathy, 5% to 10% have clinical findings consistent with myelopathy.7 Risk factors for the development of cervical spondylotic myelopathy include smoking, repetitive occupational injury involving heavy lifting, cerebral palsy, and Down syndrome.3 Hereditary factors have also been noted with findings suggestive of an increased risk in first and third degree relatives and in apolipoprotein E4 (APOE4) allele carriers.8,9 In addition, single-nucleotide pleomorphisms in collagen genes have been linked with ossification of the posterior longitudinal ligament, which causes cervical spondylotic myelopathy in up to 17% of the Asian population.10Y12 Comorbid bone disorders, which include Paget disease and the

KEY POINTS

h Cervical spondylotic disease is the most common cause of myelopathy in older patients and accounts for nearly 25% of all hospitalizations for quadriparesis.

h The pathophysiology of cervical spondylotic myelopathy is due to a combination of direct compression from spondylotic canal stenosis, dynamic stretch injury, and vascular factors.

h The incidence of cervical spondylotic myelopathy increases with advancing age and is higher in men compared with women.

Cervical spondylotic changes. Degenerative disk herniation with osteophyte formation compresses the cord from the ventral aspect. Ossification of the posterior longitudinal ligament may also impinge upon the anterior portion of the cord, while calcification or hypertrophy of the ligamentum flavum results in posterior compression. Uncovertebral hypertrophy and facet arthropathy may contribute to cord and nerve root compression as well.

FIGURE 3-1

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Myelopathy Due to Spine Diseases KEY POINTS

h Progressive gait dysfunction is one of the most common presenting symptoms in patients with cervical spondylotic myelopathy.

h Cervical spondylotic myelopathy may mimic ALS when there is a mixed picture of corticospinal tract findings and flaccid weakness in the affected segments due to anterior horn cell impingement.

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spondyloarthropathies (eg, rheumatoid arthritis and ankylosing spondylitis), can cause destructive changes of the cervical spine and supportive soft tissue structures, which further narrow the spinal canal and increase the risk of myelopathy. Diffuse idiopathic skeletal hyperostosis (known as DISH), is a common noninflammatory spondyloarthropathy that may also result in cord compression via calcification of both the anterior and posterior ligaments and reduced flexibility of the cervical spine.13,14 Clinical Manifestations Progressive gait dysfunction is one of the most common presenting symptoms in patients with cervical spondylotic myelopathy.15,16 Despite the preservation of leg strength on manual testing early on, many patients often report feelings of imbalance, stiffness, and vague sensory changes in the lower extremities. Clumsiness of the hands with difficulty performing fine motor movements (eg, buttoning a shirt, writing, or holding a coffee cup) is also prominent and may be a result of sensory loss or hand weakness. Other clinical manifestations include proximal limb weakness, especially hip flexion, and paresthesia of the hands, which may mimic carpal tunnel syndrome. Pain and stiffness in the neck, shoulder, and subscapular region may also be reported.15 Bladder disturbance manifesting as incontinence, retention, or urgency is less common and seen in only 15% to 20% of patients, which may be related to the more medial location of the descending micturition tracts topographically and dual innervation to the bladder.16 Although signs and symptoms vary depending on which anatomical structures within the cord are involved, the neurologic examination commonly demonstrates a spastic gait with diffuse corticospinal tract findings, which include increased tone, ankle clonus,

Hoffmann and Babinski signs, and limb hyperreflexia. (Sparing of the jaw jerk helps to localize the lesion caudal to the brainstem, distinguishing it from more generalized disorders affecting the corticospinal tracts, such as ALS.) Posterior column dysfunction results in large fiber sensory loss and gait instability due to reduced proprioception. Patients may also experience Lhermitte phenomenon, a sudden electric shocklike sensation in the neck that radiates down the spine with cervical flexion or Valsalva maneuver. Anterior horn cell involvement manifests as segmental lower motor neuron findings (eg, atrophy, flaccid weakness, absent or reduced reflexes) in myotomes corresponding with the level of cord compression. If the corticospinal tract is also affected, this can result in a clinical pattern mimicking ALS in which a mixed picture of atrophy and weakness occurs in the affected segments with upper motor neuron findings below the level of the lesion. Lower motor neuron abnormalities may also be seen below the level of the lesion due to changes in venous drainage related to the compression. In one report, examination of a patient with spondylotic compression at C5-C6 demonstrated atrophy of the biceps and intrinsic hand muscles, with an exaggerated triceps muscle stretch reflex.17 Other disorders with similar clinical presentations include multiple sclerosis and spinal cord ischemia (Table 3-1). Cervical spondylosis may also compress the nerve root in addition to the spinal cord, resulting in a cervical radiculomyelopathy. In these patients, the history and examination reveal sensorimotor deficits in a radicular distribution superimposed on myelopathic findings (Table 3-218). Sudden hyperextension of the neck in patients with previously asymptomatic spondylotic canal stenosis can

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TABLE 3-1 Differential Diagnosis of Cervical Spondylotic Myelopathy b ALS b Multiple sclerosis b Normal pressure hydrocephalus b Guillain-Barre´ syndrome b Hereditary spastic paraparesis b Transverse myelitis b Metabolic myelopathy: vitamin B12 deficiency, copper deficiency b Syringomyelia b Neoplasm: primary intramedullary tumor, metastatic disease b Vascular disease: spinal cord infarction or arteriovenous malformation b Infection: abscess, viral myelitis b Other primary spinal cord disorders ALS = amyotrophic lateral sclerosis.

a TABLE 3-2 Clinical Presentation in Patients With Additional Nerve Root Involvement

Root Level

Primary Muscles Affected

Motor Weakness

Sensory Changes

Reflex Loss

C3-C4

Trapezius, levator scapula, diaphragm (rare)

Scapula elevation, respiratory muscles (rare)

Occiput, jaw, upper neck (C3), proximal shoulder, lower neck (C4)

Not applicable

C5

Deltoids, biceps, brachioradialis, spinati, supinator

Shoulder abduction, external rotation, elbow flexion, forearm supination

Lateral arm over deltoid

Biceps, brachioradialis

C6

Deltoids, biceps, brachioradialis, spinati, supinator, triceps, pronator teres

Shoulder abduction, external rotation, elbow flexion and extension, forearm supination and pronation

Lateral forearm, thumb, index finger

Biceps, brachioradialis

C7

Triceps, pronator teres, extensor carpi radialis, flexor carpi radialis

Elbow and wrist extension (radial aspect), wrist flexion, forearm pronation

Index and middle finger, palm

Triceps

C8

Ulnar and median hand intrinsics, flexor pollicis longus, flexor digitorum profundus (second to fifth digits)

Finger extension, wrist extension (ulnar aspect), distal thumb and finger flexion, finger abduction and adduction

Medial forearm and hand, fourth and fifth digits

Triceps

T1

Ulnar and median hand intrinsics, flexor pollicis longus

Thumb abduction, distal thumb flexion, finger abduction and adduction

Medial forearm, fourth and fifth digits

Not applicable

a

Modified with permission from Levin KH, Continuum (Minneap Minn).18 B 2008 American Academy of Neurology. journals.lww.com/ continuum/Fulltext/2008/06000/DISEASES_OF_THE_NERVE_ROOTS.9.aspx.

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Myelopathy Due to Spine Diseases KEY POINT

h Areas of increased signal intensity within the spinal cord at the site of compression on T2-weighted MRI may represent edema, gliosis, or ischemia, while decreased signal intensity changes on T1-weighted images are suggestive of necrosis and potentially irreversible injury.

result in central cord syndrome due to buckling of the ligamentum flavum. Patients are typically older and present with acute weakness more pronounced in the arms (especially the hands). Bladder dysfunction and diffuse sensory changes below the level of the lesion may also occur. A recent MRI-based study with pathologic follow-up suggests that the main mechanism of injury is cord edema and mass effect with subsequent wallerian degeneration.19,20 Diagnosis MRI is the mainstay in the diagnostic evaluation of cervical spondylotic myelopathy, providing optimal visualization of the spinal cord, which helps to exclude tumor and other structural lesions. MRI is also useful in evaluating the intervertebral disks. While no single MRI parameter definitively indicates the presence of myelopathy in isolation of the history and clinical findings, cervical spondylotic myelopathy is more probable when the anterior-posterior diameter of the spinal canal is less than 10 mm.7 In some patients, MRI may demonstrate intramedullary signal changes at the site of compression. Areas of increased signal intensity within the spinal cord on T2-weighted images may represent edema, gliosis, or ischemia, while decreased signal intensity changes on T1-weighted images suggest necrosis and potentially irreversible injury (Case 3-1).21 Newer imaging techniques, which include diffusion tensor imaging and dynamic MRI studies evaluating the cervical spine in extension and flexion, have been found to increase the sensitivity of detecting cervical cord compression and are currently being investigated as prognostic indicators of surgical outcome.22 More recently, a specific pattern of gadolinium enhancement was described in the setting of moderate to severe cervical spondylotic myelopathy.

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In a series of 52 patients with cervical spondylosis who demonstrated a long fusiform-shaped intramedullary lesion with cord enlargement on sagittal T2-weighted imaging, a ‘‘pancakelike’’ transverse band of enhancement was seen just caudal to the site of maximal stenosis.23 On axial imaging, there was a ringlike appearance of enhancement that spared the gray matter. Despite surgical correction of the stenosis, the enhancement in most of the patients persisted for over a year.23 Although still unclear, the underlying pathology was thought to be related to focal disruption of the blood-brain barrier.23 As these radiologic findings may mimic an alternative diagnosis, such as demyelinating disease or lymphoma, careful attention to the pattern of enhancement is critical in order to avoid surgical delay or inappropriate treatment. CT myelography is best for assessing bony diseases of the spine and ligamentous calcifications, although it is still inferior to MRI for spinal cord evaluation. In addition, it is a much more invasive procedure than MRI and involves radiation exposure. However, CT myelography may be complementary and sometimes more helpful in patients with a prior history of spine surgery, especially those with hardware placement, as the metal artifact may obscure the region of interest on MRI. Likewise, for patients with pacemakers or other implanted devices that are not MRIcompatible, CT myelography is another option to consider. Although EMG is not typically used to diagnose cervical spondylotic myelopathy, it is helpful in evaluating the extent and severity of anterior horn cell involvement or concomitant root disease in patients with lower motor neuron findings. It can also detect the presence of a superimposed motor radiculopathy, which, in one high-quality-of-evidence study, was found to be predictive of the

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Case 3-1 A 58-year-old man presented with a 5-year history of progressive gait imbalance and numbness in his feet. He also reported recent onset of tingling in his hands and difficulty playing the guitar. His medical history was significant for hypertension, 30 pack-year tobacco use, and a remote fall from his truck 10 years ago, after which he started having neck pain and stiffness. Neurologic examination demonstrated nondermatomal sensory loss throughout his limbs, increased tone in his legs, and diffuse hyperreflexia. His gait was spastic and a Romberg sign was present. MRI of the cervical spine demonstrated multilevel spondylotic disease most prominent at the C3-C4 disk level, with a large posterior disk bulge and osteophytic complex causing severe canal stenosis and cord compression (Figure 3-2). The patient was instructed to stop smoking and 2 weeks later underwent C3 to C6 laminectomy and posterior spinal fusion with iliac crest autograft and screw fixation. At the 3-month follow-up examination, the sensory changes had resolved, and he was able to play the guitar again. However, his gait imbalance and hyperreflexia remained unchanged.

Sagittal T2-weighted MRI demonstrates multilevel degenerative spine disease most prominent at the C3-C4 disk level (arrow), with a large posterior disk bulge and osteophytic complex causing severe canal stenosis and cord compression. Focal T2 hyperintensity in the cord is also seen at this level, which may represent edema or gliosis.

FIGURE 3-2

Comment. Spondylotic cord compression stemming from the remote fall resulted in progressive dorsal column dysfunction with proprioceptive sensory loss manifesting as gait instability and loss of dexterity. Corticospinal tract involvement resulted in leg spasticity, further exacerbating the gait impairment. Smoking cessation was required preoperatively to reduce the risk of nonunion. Although the surgery was uncomplicated and resulted in optimal decompression, the patient was left with residual spasticity and gait dysfunction given the long-standing nature of his symptoms and degree of preoperative severity. Continuum (Minneap Minn) 2015;21(1):52–66

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Myelopathy Due to Spine Diseases KEY POINTS

h The natural history of cervical spondylotic myelopathy varies widely, although some studies have shown that most patients experience a gradually progressive course characterized by a stepwise decline. However, patients with mild disease may stabilize or even improve with conservative management.

h The most consistent predictors of poor surgical outcome are longer duration of disease and severity of symptoms; age is also be a potential negative predictor.

h Conservative treatment of cervical spondylotic myelopathy consists of stabilization with a cervical collar, pain control, intermittent bed rest, and avoidance of high-risk situations such as heavy lifting or sports that may lead to further worsening of cord compression. Gentle isometric exercises that focus on strengthening the neck flexors, as well as upper and lower limb muscles, may also be considered in combination with a cervical collar.

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development of cord compression in patients with asymptomatic cervical spondylotic disease.24 More importantly, EMG is integral in excluding potential clinical mimics, such as ALS. Somatosensory and motor evoked potentials are currently of little diagnostic value due to their low sensitivity and specificity, but, like EMG, may serve as a potential prognostic indicator.25 Prognosis The natural history of cervical spondylotic myelopathy varies widely. Some studies have demonstrated a gradual deterioration characterized by a stepwise decline, long periods of stability, or steady progression.26,27 A recent systematic review by Matz and colleagues utilizing studies with validated outcome measures found that some conservatively managed patients with mild disease (defined as a low baseline severity score) stabilized or even improved.28 Those with severe compression who had not undergone surgery, however, were found to have necrosis and gray matter cavitation at autopsy.28,29 Overall, it is estimated that 20% to 60% of nonsurgically treated patients will deteriorate over time.30 Identifying potential predictive markers of a favorable surgical outcome is key not only in helping to determine surgical versus medical management, but also in counseling patients about risks and expectations. A systematic review of 91 studies focused on prognostic indicators found that the most consistent predictors of poor surgical outcome were longer duration of disease and severity of symptoms, based on mid- to high-quality level studies.31 Age was also a potential negative predictor when only high-quality studies were included in the analysis.31 Smoking, diabetes mellitus, psychological issues, gait impairment, clumsy hands, and corticospinal tract findings had some predictive value as well.31

It is unclear if specific MRI abnormalities are predictive of clinical outcome as study results conflict in this regard as well. However, the presence of high T2signal intensity changes in association with low T1-signal intensity at the site of compression has been consistently correlated with a worse outcome postoperatively as these findings are more suggestive of necrosis, cavitation, or other signs of irreversible injury.21 In contrast, the significance of isolated T2-signal intensity changes, which may represent edema, is still controversial.21 Prognosis also appears to be worse in those with T2-signal changes spanning multiple levels. Other MRI parameters used to predict clinical outcome include various measurement ratios based on spinal canal dimensions, although the results of these studies are mixed. Management Conservative management primarily consists of stabilization with a hard or soft cervical collar, pain control, intermittent bed rest, and avoidance of highrisk situations that may lead to further worsening of cord compression. Gentle isometric exercises that focus on strengthening the neck flexors, as well as upper and lower limb muscles, may also be considered in combination with a cervical collar.32Y34 In one small study of 30 patients with mild to moderate cervical spondylotic myelopathy, a 6-week exercise program that included gait training with a treadmill, scapulothoracic exercises, and gentle neck flexor strengthening in which the patient was told to nod and flatten out the curve in the neck while lying supine resulted in improved neurologic outcome scores.34 For pain management, antiepileptics (eg, gabapentin, pregabalin), antidepressants (eg, amitriptyline, nortriptyline), nonsteroidal antiinflammatory drugs, and other analgesics

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may be helpful. Activity restrictions include the avoidance of heavy lifting (generally nothing heavier than a gallon of milk), jumping, slippery surfaces, physical overload, and any activity involving repetitive or sudden neck movements such as diving, skiing, and horseback riding. Some authors also recommend avoidance of manipulation and traction.31 While none of these individual modalities has specifically been shown to alter the natural history of myelopathy or affect the need for surgery, they can be helpful in symptomatic management. For most patients with mild myelopathy, conservative treatment may be an appropriate recommendation in combination with close monitoring for symptom progression.35 The main goals of surgical decompression are to stop further progression of the disease and preserve or improve neurologic function. Surgical options include an anterior approach, a posterior approach, and a combined anteriorposterior approach that is usually reserved for complex or multilevel disease. The anterior approach consists of a cervical diskectomy or corpectomy, a procedure that involves removal of the vertebral body. These techniques are often combined with fusion, in which a graft (either an autograft composed of the patient’s iliac crest or synthetic allograft made of titanium, plastic, or carbon) is placed in-between the vertebrae to provide structural support while the surrounding bones are allowed to fuse into one unit over time. Fusion may be further instrumented with the placement of titanium plates and screws to reduce the rate of nonunion. Posterior approach procedures include laminectomy with fusion and laminotomy, in which the lamina is partially removed and reconstructed to widen the spinal canal. Surgical decision making takes into account location of compression, alignment (kyphosis versus lordosis), and Continuum (Minneap Minn) 2015;21(1):52–66

number of levels involved.36 Age, medical comorbidities, the presence of a radiculopathy, spinal stability, smoking, axial pain, and experience of the surgeon are other variables taken into consideration. Complications vary among the different procedures and are estimated to occur at a rate of 16%; advanced age, duration of surgery, and the use of a combined approach are associated with higher rates.37,38 In addition to bleeding and infection, which can occur with all approaches, dysphagia, CSF leak, and recurrent laryngeal nerve palsy may be more common with the anterior approach, while transient C5 root distribution weakness, exacerbation of subluxation, and increased neck pain may occur more with posterior approaches.37 If an autograft is used, pain or hernia at the donor site and lateral femoral cutaneous nerve injury may be reported, whereas nonunion rates are higher in patients with allografts and those who smoke.37 To date, only three studies have compared nonoperative management with surgery for the treatment of cervical spondylotic myelopathy. The first study, a randomized controlled trial of 68 patients, addressed patients with mild myelopathy and found that those who were managed with conservative treatment consisting of immobilization with a soft collar, nonsteroidal antiinflammatory drugs, and intermittent bed rest (for those with pain) had equivalent or improved neurologic outcomes at 10-year follow-up, compared with surgically treated patients.35,39 The other two studies were nonrandomized cohort studies focused on moderate to severe myelopathy and included 62 and 101 patients with 1 and 2.5 year follow-up, respectively.40,41 Conservative management included exercises, cervical immobilization, bed rest, and cervical traction. Although a www.ContinuumJournal.com

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Myelopathy Due to Spine Diseases KEY POINT

h Treatment of cervical spondylotic myelopathy should be individualized based on clinical and diagnostic findings. Conservative therapy may be appropriate for patients with mild myelopathy, whereas surgical options should be considered for those with moderate to severe disease or rapidly progressive symptoms.

direct comparison was not made, those in the surgical group for both studies had improved neurologic outcomes at follow-up, while those treated conservatively worsened.40,41 Due to the lack of evidence derived from rigorously designed trials and an unpredictable natural history, treatment of cervical spondylotic myelopathy should be individualized based on the combination of clinical and diagnostic findings. Conservative therapy may be appropriate for some patients with mild myelopathy, whereas surgical options should be considered for those with moderate to severe disease or rapidly progressive symptoms. THORACIC AND LUMBAR SPONDYLOSIS Cord compression due to thoracic spondylotic disease is rare. While the pathophysiology is similar to that seen in the cervical and lumbar spine, thoracic disk herniation accounts for only 0.2% to 0.5% of all disk prolapses.42 In contrast, facet arthropathy, calcification of the ligaments, and congenital spine abnormalities (eg, congenital stenosis, achondroplasia) are frequent contributors to the development of thoracic spondylotic myelopathy.42Y44 Lower thoracic segments (T10 to T12) are most often affected, which may be a function of increased mobility in this region compared to the upper and midthoracic levels.42,45 Gait disturbance and neurogenic claudication are common presenting symptoms, with back pain as another prominent concern.44,45 Corticospinal tract findings, bowel and bladder abnormalities, and bilateral or asymmetric weakness and sensory changes in the lower extremities may also occur. Surgical decompression is usually recommended and may improve or stabilize neurologic function initially, although postopera-

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tive deterioration over time has been reported in a significant number of patients.42,44 Based on these findings, the overall prognosis of thoracic spondylotic myelopathy following surgery is guarded and warrants careful follow-up. A less common cause of thoracic myelopathy is idiopathic spinal cord herniation through a ventral or ventrolateral dural defect. While the clinical presentation is similar to that seen in thoracic spondylotic myelopathy with early bladder dysfunction, asymmetric weakness, and sensory deficits, a distinct imaging finding characterizes spinal cord herniation.46 In this disorder, the thoracic cord (typically from T2 to T8) abuts the posterior surface of the vertebral body, resulting in a large dorsal epidural space often mistaken for an arachnoid cyst.47 CT myelography or more dynamic MRI studies that assess CSF flow can help confirm the presence of a spinal cord herniation by demonstrating contrast leak through the deficit or changes in flow ventral and dorsal to the affected portion of the cord.47,48 In contrast to spondylotic causes of thoracic myelopathy, surgical repair of the dural defect may restore some degree of clinical function in patients with spontaneous spinal cord herniation.46,48 As the spinal cord ends at L1 to L2 in most individuals, spondylotic changes of the lumbar canal do not cause a true myelopathy, but may result in compression of the cauda equina or conus medullaris. This leads to distinct syndromes that predominantly feature bowel and bladder disturbances, lower extremity weakness, and partial corticospinal tract changes. For more information on cauda equina compression, refer to the article ‘‘Disorders of the Cauda Equina’’ by Andrew W. Tarulli, MD, in this issue . of

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SYRINGOMYELIA Syringomyelia is a cystic dilation or fluid-filled cavity within the spinal cord that typically involves the cervical region, but may extend up into the brainstem or down to the conus. Congenital syringomyelia is a result of neurulation defects and often occurs in association with Chiari malformation, tethered cord, or both.49 Acquired syringomyelia arises from a disturbance in CSF flow dynamics in which an obstructive process, such as arachnoid scarring due to trauma, inflammation, tumor, or infection, causes pressure changes and fluid accumulation within the cord leading to expansion of the central canal or formation of a new cavity. Clinical symptoms follow the destructive path of the widening syrinx, which begins in the center and expands outward and longitudinally. The classic clinical presentation of a cervical syrinx is flaccid weakness in lower cervical segments and corticospinal tract changes in the legs. Sensory loss is dependent on the cervical levels involved. With exten-

FIGURE 3-3

Continuum (Minneap Minn) 2015;21(1):52–66

sion of the syrinx in the upper segments, loss of pain and temperature sensation occurs in a capelike distribution due to injury of the decussating spinothalamic tract fibers. In the presence of lower cervical sensory loss in the upper extremities, EMG shows a characteristic pattern of C8-T1 denervation, but shows a preservation of corresponding sensory nerve responses owing to preserved continuity between dorsal root ganglion cells and their peripheral nerves. Syringomyelia may be identified with routine MRI studies, although the use of gadolinium can help exclude an underlying tumor. MRI of the brain and lumbosacral spine should also be obtained to look for a Chiari malformation and tethered cord.49 CSF flow dynamics may be evaluated using phase contrast MRI, which is useful not only for diagnosis, but also for routine monitoring and assessing response to surgical intervention.50 Treatment consists of surgical drainage with restoration of CSF flow in patients with progressive symptoms (Figure 3-3). In

KEY POINTS

h Acquired syringomyelia arises from a disturbance in CSF flow dynamics in which an obstructive process causes pressure changes and fluid accumulation within the cord leading to expansion of the central canal or formation of a new cavity.

h For patients with syringomyelia, CSF flow dynamics may be evaluated using phase contrast MRI, which is useful for diagnosis, routine monitoring, and assessing response to surgical intervention.

T2-weighted MRI demonstrates an extensive syrinx in a patient with remote trauma and history of surgical drainage. Mild degenerative spine changes are also shown.

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Myelopathy Due to Spine Diseases KEY POINTS

h Hirayama disease, or monomelic amyotrophy, primarily affects young males and is characterized by unilateral or asymmetric wasting of C7 to T1 innervated muscles of the hands and forearms.

h Flexion cervical MRI in patients with Hirayama disease may demonstrate pathologic findings of loss of dural attachment with forward displacement, posterior epidural flow void, and asymmetric cord atrophy.

patients with syringomyelia due to Chiari type I malformation, suboccipital decompression with duraplasty is typically performed (Figure 3-4). HIRAYAMA DISEASE Hirayama disease, or monomelic amyotrophy, is a rare disorder primarily affecting young males, characterized by unilateral or asymmetric wasting of C7 to T1 innervated muscles of the hands and forearms. Initially described in Asia, Hirayama disease is increasingly being recognized in the North American population. Patients typically present in the second and third decades with intrinsic hand weakness that progresses over a 5- to 6-year period and then plateaus.51,52 The proposed underlying mechanism is related to insufficient growth of the dura during childhood, which results in a tightened dural sac that is unable to accommodate the

FIGURE 3-4

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natural lengthening of the cord with neck flexion.51 As a result, the posterior dura is displaced forward on flexion, pressing the cord anteriorly against the vertebral bodies. With repetitive cord compression, chronic impairment of the arterial microcirculation in combination with venous congestion causes progressive anterior horn cell damage.52,53 Flexion cervical MRI is the test of choice to demonstrate the pathologic findings of loss of dural attachment with forward displacement, posterior epidural flow void, and asymmetric cord atrophy.53 EMG shows chronic and active (fibrillation potentials) motor axon loss changes in the affected segments. Treatment with a supportive cervical collar during the active stage of the disease has been recommended as it may prematurely terminate progression and promote clinical recovery (Case 3-2).54

Large multiloculated cervical syringomyelia in a patient with Chiari type I malformation on T2-weighted MRI.

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Case 3-2 A 23-year-old right-handed man presented with bilateral hand weakness. He first noted clumsiness of his right hand when buttoning his shirt at the age of 15. Over time, he noted progressive difficulty in both hands on performing fine motor movements, such as picking up small objects, using scissors, and opening doors. He also made more errors when typing on his keyboard and had problems turning the ignition switch in his car. There was no involvement of his legs, upper arms, or bulbar muscles, and he denied any sensory loss. Although he was starting to develop mild pain in his wrists and forearms due to musculoskeletal strain, the weakness had not changed in the last year. On neurologic examination, atrophy and weakness were seen in the hand intrinsics and distal forearms bilaterally and were much worse on the right. Muscle stretch reflexes were symmetric and normal throughout. EMG demonstrated normal sensory nerve conduction responses, but needle examination showed severe chronic motor axon loss changes in bilateral right greater than left C8 to T1 innervated myotomes with modest active denervation limited to the abductor pollicis brevis. Initial MRI cervical spine showed no abnormalities except for minimal degenerative changes and mild thinning of the cervical cord at C5-C6 (Figure 3-5A). However, follow-up flexion cervical MRI 1 month later revealed anterior shift of the spinal cord at C5-C6 with prominent anterior displacement of the dura and epidural flow voids posteriorly (Figure 3-5B). The patient was diagnosed with Hirayama disease and treated conservatively. Given the clinical plateau in the past year and the absence of significant ongoing denervation seen on EMG, the use of a cervical collar was deferred. He was instead treated with nonsteroidal anti-inflammatory drugs and neck precautions, which included avoidance of high-risk activities and proper ergonomics when sitting at his desk.

Imaging of the patient in Case 3-2. A, Sagittal T2-weighted MRI shows minimal degenerative disk changes with mild thinning of the cervical cord at C5-C6. B, Follow-up T2-weighted flexion cervical MRI 1 month later shows anterior shift of the spinal cord at C5-C6 with prominent anterior displacement of the dura and epidural flow voids posteriorly (arrows).

FIGURE 3-5

Comment. In a young man with slowly progressive unilateral or asymmetric bilateral hand wasting, the diagnosis of Hirayama disease should be suspected. EMG and flexion cervical MRI are helpful in confirming the diagnosis, but treatment is limited to conservative therapy. For patients with an active worsening of symptoms and ongoing denervation on EMG, a cervical collar may be considered.

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CONCLUSION While the clinical presentation of myelopathy due to degenerative or congenital spine disease is less acute than that of trauma or neoplastic disease, the ensuing neurologic deficits can still markedly impair quality of life and ability to perform activities of daily living. Early recognition with timely institution of the appropriate surgical or medical management remains essential in preserving clinical function. REFERENCES 1. Young WF. Cervical spondylotic myelopathy: a common cause of spinal cord dysfunction in older persons. Am Fam Physician 2000;62(5):1064Y1073. 2. Moore AP, Blumhardt LD. A prospective survey of the causes of non-traumatic spastic paraparesis and tetraparesis in 585 patients. Spinal Cord 1997;35(6):361Y367. doi:10.1038/ sj.sc.3100422. 3. Baron EM, Young WF. Cervical spondylotic myelopathy: a brief review of its pathophysiology, clinical course, and diagnosis. Neurosurgery 2007;60(1 suppl 1):S35YS41. doi:10.1227/ 01.NEU.0000215383.64386.82. 4. Henderson FC, Geddes JF, Vaccaro AR, et al. Stretch-associated injury in cervical spondylotic myelopathy: new concept and review. Neurosurgery 2005;56(5):1101Y1113. doi:10.1227/01.NEU.0000157929.85251.7C. 5. Kalsi-Ryan S, Karadimas SK, Fehlings MG. Cervical spondylotic myelopathy the clinical phenomenon and the current pathobiology of an increasingly prevalent and devastating disorder. Neuroscientist 2013;19(4):409Y421. doi:10.1177/1073858412467377. 6. Shedid D, Benzel EC. Cervical spondylosis anatomy: pathophysiology and biomechanics. Neurosurgery 2007;60(1 suppl 1):S7YS13. doi:10.1227/01.NEU.0000215430.86569. 7. Levin KH. Cervical spondylotic myelopathy. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. Accessed October 15, 2014. 8. Patel AA, Spiker WR, Daubs M, et al. Evidence of an inherited predisposition for cervical spondylotic myelopathy. Spine 2012;37(1): 26Y29. doi:10.1097/BRS.0b013e3182102ede. 9. Setzer M, Hermann E, Seifert V, Marquardt G. Apolipoprotein E gene polymorphism and the risk of cervical myelopathy in patients with chronic spinal cord compression. Spine (Phila Pa 1976) 2008;33(5):497Y502. doi:10.1097/BRS.0b013e3181657cf7.

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Myelopathy due to degenerative and structural spine diseases.

This article reviews the current evaluation and treatment of patients with myelopathy due to cervical spondylotic disease and other structural disorde...
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