PRIMARY MYELOPATHIES (DEGENERATIVE, INFECTIVE, METABOLIC)

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CHAPTER 39 PRIMARY MYELOPATHIES (DEGENERATIVE, INFECTIVE, METABOLIC)

A number of conditions may selectively involve the spinal cord; some of these conditions also involve other neural tissues, to a lesser extent. The spinal cord neurons are relatively extensive, and as a result, they may be particularly susceptible to defects, which impair intraneuronal transport mechanisms. This chapter covers primary disorders of the spinal cord, excluding spinal cord trauma, spinal cord compression, and developmental spinal disorders; those topics are covered in Chapters 38, 40, and 99. For discussion, it is convenient to divide the primary myelopathies into acute (including subacute) and chronic clinical manifestations.

ACUTE MYELOPATHIES

Acute myelopathy, or acute transverse myelopathy, is a disorder of acute or subacute spinal cord dysfunction resulting from a variety of causes, as listed in Table 39-1. In a clinical study, de Seze and colleagues (2001) found the commonest cause to be multiple sclerosis (43%); other causes included systemic disease (16.5%), spinal cord infarction (14%), infectious or parainfectious conditions (6%), and radiation myelopathy (4%). No underlying cause was found in the remaining 16.5%, despite an average of 29 months’ follow-up. The criteria for the clinical diagnosis of acute transverse myelopathy include (1) acute/subacute onset of sensory and motor symptoms, including symptoms of sphincter dysfunction; (2) spinal segmental level of sensory disturbance with a well-defined upper limit; (3) occurrence of symptoms over no more than 3 weeks and sustained for a period of at least 48 hours; (4) no clinical or radiological evidence of spinal cord compression; and (5) no known history of neurological disease or neurological symptoms.

TABLE 39-1 Causes of Acute Transverse Myelopathy

Demyelination Multiple sclerosis, acute disseminated encephalomyelitis, neuromyelitis optica
Systemic disorders Systemic lupus erythematosus, sarcoid, Sjögren’s syndrome, Behçet’s syndrome, antiphospholipid syndrome, mixed connective tissue disease
Infectious/parainfectious Herpes simplex viruses 1 and 2, herpes zoster virus, Epstein-Barr virus, cytomegalovirus, human herpesvirus 6, enterovirus, human immunodeficiency virus, human T cell lymphotrophic virus type 1, mycoplasma, Lyme disease, syphilis
Vascular Arterial, venous, watershed, arteriovenous malformation, fibrocartilaginous embolism
Miscellaneous Idiopathic Radiation myelopathy, epidural lipomatosis

New cases of acute transverse myelopathy occur at a rate of 1 to 4 per million people per year. There is no gender predisposition, in contrast to the predominant female predisposition in multiple sclerosis. Fifty percent of patients develop almost complete paraparesis, most have bladder dysfunction, and 80% to 94% have sensory disturbance. The recovery of the neurological deficit is somewhat variable: One third of patients recover with little or no deficit, one third have moderate disability, and one third have severe disability.

Acute transverse myelopathy may be an initial presenting feature of multiple sclerosis. Typically, such patients who ultimately go on to develop multiple sclerosis have an asymmetrical partial transverse myelitis: that is, predominant sensory disturbance with relative motor sparing. Magnetic resonance imaging (MRI) of the spine characteristically shows lesions extending over less than two spinal segments. MRI of the brain may show characteristic demyelinating lesions (in up to 50% of cases manifesting as a clinically isolated syndrome). The cerebrospinal fluid may reveal unmatched oligoclonal bands (in up to 50% of cases manifesting as a clinically isolated syndrome).

The diagnostic evaluation of a patient with suspected acute transverse myelopathy initially involves neuroimaging of the spine (usually MRI with gadolinium) to rule out a compressive myelopathy. After a compressive spinal lesion is ruled out, a lumbar puncture helps distinguish an inflammatory myelopathy from a noninflammatory myelopathy. The cerebrospinal fluid analysis includes a cell count determination and differential, protein and glucose level measurements, oligoclonal band analysis, and cytologic studies. If an inflammatory myelopathy is suspected, brain MRI and evoked potentials may indicate whether there is a multifocal inflammatory process, suggestive of multiple sclerosis, acute disseminated encephalomyelitis or neuromyelitis optica (also known as Devic’s syndrome). In the case of neuromyelitis optica, patients may be tested for a specific neuromyelitis optica-immunoglobulin G autoantibody, as recently described by Lennon and associates.

A possible infectious/parainfectious cause may manifest with certain clinical features: fever, rash, meningismus, concurrent systemic infection, immunocompromised state, recurrent genital infection, radicular burning pain with vesicles (suggestive of herpes zoster), and lymphadenopathy. In such cases, further investigation includes serum and cerebrospinal fluid viral and bacterial cultures, cerebrospinal fluid viral and bacterial polymerase chain reaction studies, and acute and convalescent serum antibody studies for the infectious agents listed in Table 39-1.

Alternatively, certain clinical features such as arthritis, erythema nodosum, xerostomia, Raynaud’s phenomenon, rash, and ulcers may be suggestive of an underlying systemic disease, such as systemic lupus erythematosus, Sjögren’s syndrome, sarcoidosis, mixed connective tissue disease, Behçet’s disease, or antiphospholipid antibody syndrome. If a systemic autoimmune disease is suspected, serum should be analyzed for antinuclear antibodies, double-stranded DNA antibodies, Ro and La antibodies, cardiolipin antibodies, lupus anticoagulant, angiotensin-converting enzyme level, β2-glycoprotein level, and complement levels. Schirmer’s test, lip/salivary gland biopsy, and chest computed tomographic scan should also be considered.