The Chronic Inactive MS Lesion

The MS lesion may evolve differently during "early" and "chronic" phases of the disease. Different stages and types of demyelinating activity can be identified within these phases. Most neuropathological studies of MS are based on tissue from individuals with long-standing disease. Pathologically, these late chronic cases are characterized by the presence of multiple sharply demarcated plaques of demyelination typically ranging from <1 mm to several centimeters in size. Plaques are present in both white and gray matter, with a predilection for the periventricular white matter, optic nerves, brainstem, cerebellum, and spinal cord (3). By gross inspection, the plaques appear as circumscribed, slightly depressed gray colored areas with

Multiple Sclerosis Lesions

Figure 1 (See color insert.) Chronic multiple sclerosis. Grossly, plaques appear as well-circumscribed, slightly depressed gray areas of increased tissue texture. The chronic inactive plaque microscopically appears as a sharply circumscribed area of myelin pallor (A, LFB/PAS) with variable reduction in axonal density (B, neurofilament protein). The lesions are hypocel-lular and lack macrophages containing myelin debris (C, KiMlP for macrophages). Abbreviation: LFB/PAS, luxol fast blue/periodic acid schif.

Figure 1 (See color insert.) Chronic multiple sclerosis. Grossly, plaques appear as well-circumscribed, slightly depressed gray areas of increased tissue texture. The chronic inactive plaque microscopically appears as a sharply circumscribed area of myelin pallor (A, LFB/PAS) with variable reduction in axonal density (B, neurofilament protein). The lesions are hypocel-lular and lack macrophages containing myelin debris (C, KiMlP for macrophages). Abbreviation: LFB/PAS, luxol fast blue/periodic acid schif.

increased tissue texture (Figure 1). The lesions may be round or oval, but frequently show finger-like extensions that may follow the path of small or medium sized vessels (4). Microscopically, the chronic inactive MS plaque appears as a sharply circumscribed, relatively hypocellular, pale area with marked myelin loss, prominent fibril-lary astrocytosis, and variably reduced axonal density (Figure 1A-C). There is no evidence of active myelin-breakdown, and mature oligodendrocytes are markedly diminished or absent from chronic inactive lesions. Variable but usually scant chronic inflammatory infiltrates consisting of T-lymphocytes and macrophages may still be present, particularly in the perivascular regions.

0 0

Post a comment