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A demyelinating disease is any disease in which the myelin sheath of the neuron is damaged. Weakening of the transmitted electrical signal ultimately results in impairment in sensation, cognition, and movement or other functions depending on which nerves are affected. Classification of demyelinating diseases is made based on whether the nerves affected are of the central nervous system or of the peripheral nervous system (Table 130-1).
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The causes of demyelinating diseases are multifactorial. Myelin destruction may be caused by autoimmune reactions (eg, multiple sclerosis), inflammation (eg, optic neuritis, transverse myelitis, disseminated encephalomyelitis), or infectious agents (eg, Creutzfeldt-Jakob viral infection of oligodendrocytes). In addition, there is a genomic component to demyelinating diseases. Inherited metabolic disorders affect myelin synthesis/turnover; these diseases are termed leukodystrophies. Other causes of demyelinating diseases involve neuroleptics, and certain chemicals such as organophosphates. Lysophosphatidylcholine or lysolecithins, found in foods and cosmetics with lecithin treated with the enzyme phospholipase, also cause demyelination.
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CENTRAL NERVOUS SYSTEM DEMYELINATING DISEASES
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A condition defined by demyelinating inflammation of the optic nerve that often occurs in association with multiple sclerosis and Devic’s disease (neuromyelitis optica). Visual recovery begins within a few weeks. Thirty percent of adults develop multiple sclerosis within 5 years of presenting with optic myelitis. Treatment with intravenous (IV) methylprednisolone is indicated for patients with either severe vision loss or two or more white matter lesions in MRI.
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Transverse Myelitis (TM)
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TM is a rare inflammatory disorder causing injury across both sides of one level or segment of the spinal cord, resulting in various degrees of weakness, sensory alterations, and autonomic dysfunction. TM usually occurs as a postinfectious complication and presumably results from an autoimmune process. However, TM also can be associated with infectious, systemic inflammatory, or multifocal CNS diseases. TM affects people of all ages, with bimodal peaks at 10–19 and 30–39 years and 25% of cases in children. Approximately 70%–90% of cases are monophasic, and a small percentage experience recurrent disease if a predisposing underlying disease is present. Treatment for acute idiopathic TM is high-dose IV glucocorticoids, such as methylprednisolone or dexamethasone, for 3–5 days. Treatment for acute TM complicated by motor involvement is steroid plus plasma exchange.
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Multiple Sclerosis (MS)
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MS is an autoimmune demyelinating disorder with a genetic predisposition characterized by distinct episodes of neurological deficits that affect the brain and ...