Chapter 7 Pathology and Pathogenesis of Multiple Sclerosis

Abstract

This chapter discusses the pathology and pathogenesis of multiple sclerosis (MS). The basic pathological feature unique to MS is the presence of multifocal demyelinated plaques. These focal areas of myelin destruction occur on a background of an inflammatory reaction consisting predominantly of macrophages and T lymphocytes. MS lesions can be characterized as active or inactive. Macrophage activation and phagocytosis of myelin proteins in the lesions are reliable indicators of ongoing demyelinating activity. Active lesions are heavily infiltrated by macrophages containing myelin debris, which are often closely associated with the disintegrating myelin sheath. The chronic inactive MS plaque is a sharply circumscribed hypocellular plaque with no evidence of active myelin breakdown. Fibrillary gliosis is prominent and axonal density is often markedly reduced. Oligodendrocytes are markedly diminished or absent from chronic inactive lesions. Variable degrees of inflammation may, however, still be present, particularly in the perivascular region. Neuropathological studies of MS lesions have clearly demonstrated the presence of remyelination.