Disorders of myelin

Abstract

The chapter begins with a discussion of common major clinical features and mechanisms of damage to myelin. Myelin is produced in the peripheral nervous system (PNS) by Schwann cells and in the central nervous system (CNS) by oligodendrocytes. Key functions of myelin are to house axons and to provide for the axons hollow tubular channels of extracellular matrix, provide physical strength to the axon, insulate the axon from environmental toxins, and allow saltatory conduction increasing nerve conduction velocity as much as 100-fold. The four major mechanisms of demyelination are death of oligodendrocyte or Schwann cell, interference with myelin synthesis, interference with myelin turnover, and immune-mediated destruction of myelin. In the CNS, myelin tracts commonly damaged are the corticospinal tract (weakness, spasticity), spinothalamic tract (sensory loss), visual pathway (visual disturbance), and spinocerebellar pathways (ataxia). In the PNS, motor (flaccid weakness) and sensory (position sense loss) are often involved. The chapter then discusses multiple sclerosis, neuromyelitis optica, acute disseminated encephalomyelitis, and Guillain-Barré syndrome, with attention to their pathophysiology, major clinical features, major laboratory findings, and principles of management and prognosis.