The onset and progression of the lesion in multiple sclerosis.

The active established plaque in multiple sclerosis is characterized by hypercellularity at its edge and lipid phagocytosis (gitter cells). The hyperactive early plaque shows cells throughout the lesion. Active plaques seems to extend at their edges; proteolysis of myelin basic protein is perhaps an important factor in the myelin breakdown at the rim of these lesions. The hyperactive early plaque usually shows infiltration with monocytes, lymphocytes and plasma cells around its central vein. The phagocytic element is presumably a response to myelin breakdown but the significance of the lymphocytes in these lesions in uncertain. Perivenular infiltrates that are predominantly composed of lymphocytes are seen around veins and venules in the vicinity of established lesions in some patients who died during an acute episode...