Neuromyelitis Optica

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Neuromyelitis optica (NMO) is an uncommon neurological illness characterized by the occurrence of optic neuropathy and myelopathy in close temporal relationship. The separation from MS has become questioned, owing to the frequent dissemination of lesions outside the optic nerves and spinal cord. Part of the difficulty lies with the broad, imprecise, and inconsistent definition. The names Devic's syndrome, Devic's disease, and NMO are often used interchangeably, although the first name encompasses all patients who fit the above definition and the second and third should only be used to refer to those patients presumed to have a distinct disorder. The term opticospinal MS is often used in the Far East to denote patients with exclusive or predominant involvement of optic nerves and spinal cord, encompassing most patients with Devic's syndrome.

Pathogenesis and Pathophysiology. Devic's syndrome may occur with ADEM, autoimmune disorders, MS, and possibly viral infections. Not surprisingly, the pathological descriptions are quite varied because these patients are invariably a heterogeneous group. Classically, acute spinal cord lesions demonstrate diffuse swelling and softening that extend over several levels or involve nearly the entire

cord in a continuous or patchy distribution. Acutely, there is destruction with dense macrophage infiltration involving white and gray matter, loss of myelin and axons, and lymphocytic cuffing of vessels. In chronic lesions, the cord is atrophic and necrotic, with cystic degeneration and gliosis. In the absence of perivascular cuffing, these extensive lesions resemble infarctions. The prominent spinal cord swelling in the confines of the restrictive pia presumably may raise intramedullary pressure, leading to the collapse of small parenchymal vessels, further propagating tissue injury. Proliferation of vessels with thickened and hyalinized walls similar to that seen after infarction or other extensive injury may occur.y Less fulminant lesions commonly coexist and are much more typical of inflammatory demyelination. The optic nerves, chiasm, and occasionally cerebral hemispheres are involved in a similar fashion with either demyelinating lesions, necrotizing lesions, or both.

Epidemiology and Risk Factors. Devic's syndrome occurs in patients of varied ages (range, 1 to 73). The mean age at onset of monophasic Devic's syndrome is 27, whereas relapsing NMO (see later) tends to occur in an older age group (mean age at onset of 43). Monophasic Devic's syndrome affects males and females equally, whereas relapsing NMO affects females predominantly (F:M, 3.8:1). One third of patients have a preceding infection within a few weeks of neurological symptom onset. Most commonly this is a nonspecific upper respiratory tract infection, flu, or gastroenteritis. The most common specific infections preceding the development of Devic's syndrome are chickenpox and pulmonary tuberculosis. Devic's syndrome has also followed vaccination for swine flu and mumps. Only a few instances of the familial occurrence of Devic's syndrome have been reported, and in one of these families a unique mitochondrial mutation was found. Devic's syndrome is said to be more common in Japan and East Asia, although even there it is uncommon (less than 5 per 100,000).

Clinical Features and Associated Findings. Symptoms of optic neuritis and myelitis develop over hours to days and are often preceded or accompanied by headache, nausea, somnolence, fever, or myalgias. Continued progression of symptoms over weeks or months occasionally occurs. Most patients (greater than 80 percent) develop bilateral optic neuritis. Bitemporal or junctional field deficits, indicating chiasm involvement, are sometimes present early in the course of the optic neuritis. Visual loss is often accompanied by periocular pain, and myelitis onset is sometimes heralded by localized back or radicular pain. Lhermitte's sign is common. Severe degrees of neurological deficits are usual, and the degree of recovery is variable.

Patients who present with Devic's syndrome can follow one of several possible courses. Approximately 35 percent have a monophasic illness, 55 percent develop relapses nearly limited to the optic nerves and spinal cord (relapsing NMO or opticospinal MS), and rarely patients have a fulminantly progressive course without relapses or a course typical of MS.y Relapsing NMO is often associated with autoimmune disorders, most commonly systemic lupus erythematosus. These patients also frequently have an elevated erythrocyte sedimentation rate and nonspecific elevation of autoantibodies, including antinuclear antibodies, anti-dsDNA, and antiphospholipid antibodies. Tonic spasms and neuropathic lower extremity pain are common sequelae to the spinal cord damage. Symptoms referable to brain stem lesions (nystagmus, ophthalmoparesis, vertigo) can occur in these patients as well.

Differential Diagnosis. The differential diagnoses for Devic's syndrome includes MS, ADEM, pulmonary tuberculosis, and viral infection (especially in the immunocompromised patient). In patients with an apparent affected family member, consideration should be given to mitochondrial disease. Relapsing NMO should raise the suspicion for associated autoimmune disorders. Because Devic's syndrome can occur in persons older than the age of 60, when an unrelated ischemic optic neuropathy could occur, and because isolated or recurrent myelopathy may precede the optic neuritis, additional consideration must be given to spinal cord compression, spinal cord tumor, and spinal arteriovascular malformation or dural fistula.

Evaluation. Imaging is needed to exclude structural lesions and provide information on the pathological process. Optic nerve or chiasm enlargement, T2-weighted signal changes, and enhancement may be seen on head MRI during the acute phase. Increased T2-weighted signal in the medulla is not uncommon and usually represents extension of high cervical lesions. Cerebral white matter lesions can be seen on head MRI in about 25 percent of cases. Spine MRI characteristically shows cord swelling, signal changes, and enhancement extending over several levels ( F.igr,48z4 ). This appearance may resemble a spinal cord tumor, prompting consideration for biopsy. An occasional patient may need prone and supine myelography to exclude a spinal dural-based AVM. Laboratory investigations reveal an elevated erythrocyte sedimentation rate in one third, positive antinuclear antibodies in nearly one half, and occasionally other autoantibodies. y It is reasonable to exclude syphilis, Lyme disease, and human immunodeficiency virus by laboratory testing. A chest radiograph helps to exclude pulmonary tuberculosis and sarcoidosis. CSF examination is an essential part of the evaluation for Devic's syndrome, and repeated studies are sometimes necessary to ensure that there is no infection in that the CSF findings are sometimes atypical for inflammatory demyelination. In contrast to MS, a minority of patients with Devic's syndrome (17 percent) have a normocellular CSF during the acute phase. A marked pleocytosis is often present, sometimes exceeding 100 cells. Moreover, neutrophils are commonly seen in CSF and may predominate, a situation virtually unknown in MS. y , y The protein concentration is often very high and in 41 percent exceeds 100 mg/dl. Despite the intense inflammatory response, OCBs are conspicuously absent in the majority, being present in fewer than 20 percent of patients. CSF serology for the herpesvirus family (HSV types 1 and 2, varicella-zoster virus, Epstein-Barr virus, and cytomegaloviruses) is important, and polymerase chain reaction testing should be done in cases suggestive of viral infection (immunocompromised patients).

Management. Patients with acute or subacute Devic's syndrome often respond to corticosteroids (e.g., intravenous methylprednisolone). Limited experience suggest that they may respond to plasma exchange even when intravenous methylprednisolone does not produce significant improvement. Attempts at preventing relapses and the subsequent

Figure 48-4 Spine MRI of patients with relapsing NMO// , Sagittal T2-image of the cervical spine showing cord expansion and signal abnormalities extending through the cervical and upper thoracic B, T1-weighted sagittal MRI showing cord swelling and extensive gadolinium enhancement from C1 to C7. Further enhancement is seen in the upper thoracic aC and D, Sagittal T2-weighted spine MRI showing a diffuse hyperintense lesion extending from T1 to the conus.

disability are often disappointing even with the use of immunosuppressive agents (e.g., azathioprine, cyclophosphamide).

Supportive care is a mainstay of management. Patients with Devic's syndrome are prone to many complications and require measures to prevent deep venous thrombosis and pulmonary embolism, urinary tract infection, decubiti, and contractures. Mechanical ventilation may be needed either temporarily or permanently. Patients with monophasic Devic's syndrome generally have simultaneous or rapid onset of the optic neuritis and myelitis (interval usually less than 1 month). Although some have significant residual disability, many recover remarkably and have little or no permanent deficits. A history of previous vague neurological symptoms or definite demyelinating events is predictive of future relapses, either typical of MS or relapsing NMO. Those patients destined for recurrent myelitis and optic neuritis have a longer interval between the onsets of myelitis and optic neuritis. The vast majority of patients with relapsing NMO have very aggressive disease with frequent and severe exacerbations and a poor prognosis.

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