neurologic disorders
Overview of Demyelinating Disorders
Introduction
Myelin sheaths cover many nerve fibers in the central and peripheral nervous system; they accelerate axonal transmission of neural impulses. Disorders that affect myelin interrupt nerve transmission; symptoms may reflect deficits in any part of the nervous system. Myelin formed by oligodendroglia in the central nervous system (CNS) differs chemically and immunologically from that formed by Schwann cells peripherally. Thus, some myelin disorders (eg, Guillain-Barré Syndrome (GBS) , Demyelination is often secondary to an infectious, an ischemic, a metabolic, or a hereditary disorder or to a toxin (eg, alcohol,ethambutol). In primary demyelinating disorders, cause is unknown, but an autoimmune mechanism is suspected because the disorder sometimes follows a viral infection or viral vaccination. Demyelination tends to be segmental or patchy, affecting multiple areas simultaneously or sequentially. Remyelination often occurs, with repair, regeneration, and complete recovery of neural function. However, extensive myelin loss is usually followed by axonal degeneration and often cell body degeneration; both may be irreversible. Demyelination should be considered in any patient with unexplained neurologic deficits. Primary demyelinating disorders are suggested by the following: Diffuse or multifocal deficits Sudden or subacute onset, particularly in young adults Onset within weeks of an infection or vaccination Deficits that wax and wane Symptoms suggesting a specific demyelinating disorder (eg, unexplained optic neuritis or internuclear ophthalmoplegia suggesting multiple sclerosis) Specific tests and treatment depend on the specific disorder. 