Acquired and Hereditary Myelopathies
Natalie R. Weathered
Noam Y. Harel
INTRODUCTION
Myelopathy indicates pathology of the spinal cord leading to dysfunction of central motor and sensory circuits, as opposed to radiculopathy (pathology of spinal roots), which affects solely peripheral circuits. A large number of conditions may cause myelopathy (Table 111.1). This chapter expands on key inflammatory, infectious, vascular, metabolic, genetic, and toxic insults.
SYRINGOMYELIA
A syrinx is an intramedullary fluid-filled cavity typically found within the cervical to midthoracic spinal cord (Fig. 111.1), but extension down to the conus medullaris is also possible as is upward extension to the brain stem in which case it is called syringobulbia. The cavity is most commonly filled with cerebrospinal fluid (CSF). However, syringomyelia should be regarded as distinct from simple cystic expansion of the central canal for which the term hydromyelia applies.
EPIDEMIOLOGY
The prevalence of syringomyelia in Western countries is approximately 8.4 cases per 100,000. It typically presents in the third to fourth decade of life, and men are more frequently affected than women. It is uncommon in childhood or late-adult years.
PATHOBIOLOGY
Generally speaking, primary syringomyelia arises from an impairment of normal CSF flow dynamics. Although congenital cases of primary syringomyelia do exist, syringomyelia more often arises secondary to Arnold-Chiari type 1 malformation. There has long been debate about exactly how this posterior malformation leads to syringomyelia, with no definite consensus on a single theory. Spinal cord tumors may also cause secondary syringomyelia by altering local CSF flow dynamics. Additionally, syringomyelia may be seen in the chronic phase after trauma, either as an ex vacuo lesion that persists after absorption of an intramedullary hematoma or due to local inflammation of the pia-arachnoid resulting in adhesions between the meninges and spinal cord. In animal models, these adhesions lead to ischemia, demyelination, and ultimately, cavitation.
CLINICAL FEATURES
The classic presentation of cervicothoracic syringomyelia is a capelike distribution of decreased pain and temperature sensation in the back, arms, and hands, which occurs due to disruption of the crossing spinothalamic tracts. There may be varying degrees of weakness in the arms (lower motor neuron type due to involvement of cervical anterior horn cells) and legs (upper motor neuron type due to involvement of lateral corticospinal fibers). A Horner syndrome may be present if a cervicothoracic syrinx affects the intermediolateral columns. Bowel and bladder function are generally preserved unless the syrinx extends toward the sacral cord segments.
DIAGNOSIS
Magnetic resonance imaging (MRI) allows visualization not only of the syrinx but also of any associated abnormalities such as Arnold-Chiari malformation, neoplasm, or arachnoid granulations. Full cord imaging should be strongly considered. MRI CSF flow studies may also be useful in guiding treatment. There are no biomarkers associated with syringomyelia. CSF is often normal or may have a nonspecific, mild elevation in protein.
TREATMENT
Conservative observation is warranted in cases with no or only minor symptoms and in cases of Arnold-Chiari malformation with tonsillar herniation less than 5 mm below the foramen magnum in the setting of normal CSF flow studies. In more severe cases of Arnold-Chiari, however, posterior fossa decompression and cervical laminectomy with or without duraplasty is frequently pursued in hopes of restoring normal CSF flow dynamics.
In cases of syringomyelia secondary to neoplasm, if resection is not possible, then fenestration or marsupialization of the syrinx may be attempted. Lysis of adhesions and/or shunting of the syrinx to the pleural or peritoneal cavities is also performed, although the benefits have not been proven and are very difficult to predict in individual patients.
OUTCOME
A recent study by Alfieri and Pinna found that surgical decompression for Arnold-Chiari type 1 malformation associated with syringomyelia tends to be well tolerated with few complications. Additionally, 93.4% of patients experienced some degree of clinical improvement.
In contrast, a study of surgical treatment for posttraumatic syringomyelia showed much lower clinical success rates, with only 51% of patients reporting clinical improvement. Forty-one percent of patients experienced no clinical change, and 8% had further clinical deterioration. Notably, among those patients in whom surgery was not recommended based on lack of significant neurologic symptoms, 84% remained stable at 10 years. The high progression-free rate and the unsure evidence for surgical efficacy both argue for the clinician to take a conservative, watchful approach to posttraumatic syringomyelia if at all possible.
METASTATIC CORD COMPRESSION
Neoplasm should be high on the differential anytime someone presents with a previously undiagnosed myelopathy. Metastatic disease is much more common than a primary central nervous system (CNS) tumor. In fact, an estimated 12% to 20% of patients
with cancer present with spinal metastasis as the initial symptom. Primary spinal cord tumors are much rarer, with an estimated incidence of 0.74 cases per 100,000—these neoplasms are discussed elsewhere in this volume. Further information on metastatic neoplasm may also be reviewed in Chapter 97.
with cancer present with spinal metastasis as the initial symptom. Primary spinal cord tumors are much rarer, with an estimated incidence of 0.74 cases per 100,000—these neoplasms are discussed elsewhere in this volume. Further information on metastatic neoplasm may also be reviewed in Chapter 97.
TABLE 111.1 Differential Diagnosis of Myelopathy | ||||||||||||||||||
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 FIGURE 111.1 Syringomyelia on a T2-weighted MRI. The syrinx, which appears as a high-intensity linear lesion in the central cord, extends from C4 to C7. (From Peleggi AF, Lovely TJ. Treatment of delayed Chiari malformation and syringomyelia after lumboperitoneal shunt placement: case report and treatment recommendations. Surg Neurol Int. 2012;3:101, with permission.) |
It is important to bear in mind that not all myelopathy in the setting of neoplasm is a direct consequence of the neoplasm itself but rather may be secondary to radiation injury, chemotherapy toxicity, or a paraneoplastic disorder.
EPIDEMIOLOGY
The cancers that most frequently metastasize to the spinal column are lung, breast, renal, hematopoietic, melanoma, prostate, and gastrointestinal. At least 95% of spinal metastases are extradural, usually to the vertebrae, and may remain asymptomatic. Autopsy studies suggest that over 30% of patients with advanced systemic cancer have pathologic evidence of vertebral metastases at the time of death. In the rostrocaudal axis, the majority of spinal metastases localize to the lumbar spine. However, due to the narrower diameter of the spinal canal within the thoracic segments, most symptomatic metastases are within the thoracic spine.
PATHOBIOLOGY
Most spinal metastases travel hematologically either through the arterial system or retrogradely through Batson venous plexus. As the vertebral column comprises a large proportion of the body’s bone marrow rich in growth factors, the vertebrae may provide a particularly hospitable environment for metastatic cells. Leptomeningeal metastases can also result from either extension from nearby bone or spread through the CSF.
CLINICAL FEATURES
In addition to the usual myelopathic symptoms of weakness, sensory loss, and urogenital dysfunction, spinal neoplasms are often marked by pain. The pain may be local or radicular. It may accompany myelopathic symptoms acutely, or it may precede myelopathic symptoms by weeks to months. Although nonspecific, red flags of concern for a cancerous cause of back pain include age older than 60 years, associated weight loss, worse at night, thoracic rather than lumbar pain, and tenderness to palpation. The rate of symptom progression may range from slowly progressive
(as a result of compressive tumor growth) to an acute onset (such as a pathologic vertebral fracture secondary to intravertebral tumor). In addition, metastases may alter arterial perfusion and/or venous drainage, resulting in acute ischemia, hemorrhage, or venous compression.
(as a result of compressive tumor growth) to an acute onset (such as a pathologic vertebral fracture secondary to intravertebral tumor). In addition, metastases may alter arterial perfusion and/or venous drainage, resulting in acute ischemia, hemorrhage, or venous compression.
DIAGNOSIS
Although a computed tomography scan performs well at detecting bony metastases, MRI with contrast remains the test of choice, as it visualizes the extent of cord and soft-tissue involvement, as well as vasogenic and cytotoxic edema. If a neoplasm is identified, full neuraxis imaging should be completed to evaluate for additional lesions, as these may alter treatment and prognosis. Additionally, if the patient is not otherwise known to have cancer, then a full assessment for the primary tumor should be initiated. If the spinal lesion is intradural, a high-volume lumbar puncture should be sent for cytology and flow cytometry although the sensitivity of these studies is not high. Ultimately, biopsy of either the spinal lesion or a suspected primary tumor source if easier to access remains the diagnostic gold standard.
TREATMENT
The mainstay of treatment has traditionally been glucocorticoid and radiation therapy. Radiation tends to be well tolerated, and 65% to 80% of patients report improvement of symptoms. Highdose corticosteroids such as dexamethasone 100 mg intravenous push (IVP), followed by 10 mg every 6 hours with a rapid taper over the next few days, is often used concurrently for symptom management. A randomized trial has shown that decompressive surgical resection plus radiation therapy for acute paraplegia results in greater ability to walk (84% vs. 57%), and a better chance of regaining the ability to walk (62% vs. 19%), compared to radiation therapy alone [Level 1].1
OUTCOME
As mentioned, the prognosis after diagnosis of a spinal metastasis is poor, with an average life expectancy of 4 to 15 months. The emphasis in management, therefore, is typically in maintaining the highest quality of life possible.
INFECTIOUS MYELOPATHY
Numerous infectious causes of myelopathy may induce symptoms through direct neuroinvasion, compression, or as an inflammatory response. Symptoms may occur at the time of the acute infection, as in the case of viral myelitis, meningoencephalitis, or abscess, or they may be delayed by days to weeks as in the case of postinfectious or postvaccination myelitis or even years in the case of neurosyphilis or HIV.
This chapter expands on viral myelitis and human T-cell lymphotropic virus (HTLV)-associated myelitis. Many other infectious syndromes are detailed elsewhere in this book. Additional reference may be made to Chapters 61 to 67.
VIRAL MYELITIS
Epidemiology
The true incidence of viral myelitis is unknown. Worldwide, the viral syndrome of acute flaccid paralysis, one form of viral myelitis, occurs in approximately 40 per 1,000,000 individuals per year. Prior to widespread vaccination, polio accounted for the vast majority of cases of acute flaccid paralysis. In recent times, West Nile virus (WNV) and Japanese encephalitis are the more likely culprits. Cases of transverse myelitis number approximately 1 to 4 cases per 1,000,000 individuals per year. Viral myelitis tends to be more common in the summer and early fall with a bimodal incidence peak in adolescence and the fourth decade of life.
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