Walsh & Hoyt: Pathology

The neuropathologic findings in acute EL include inflammation, vasculopathy, and necrosis, consistent with viral infection. The leptomeninges show vascular congestion, with hyperemia and petechiae. Cerebral edema is present. Microscopic features of the acute infection are diffuse perivascular cuffing with lymphocytes and plasma cells. Congestion and minute hemorrhages in gray matter result from destruction of small venules. Diffuse parenchymal inflammation is composed of lymphocytes, plasma cells, and inflammatory nodules. In addition, many specimens show focal meningeal infiltration, neuronophagia, and loss of neurons with release of neuromelanin pigment into the neuropil of the locus ceruleus, cerebellum, ocular motor nuclei, and pars compacta of the substantia nigra. Chronic cases show extensive astrogliosis, especially in frontal and temporal white matter, persistent perivascular infiltrates, and, occasionally, perivascular or intraparenchymal mineralization in the striatum, hippocampus, thalamus, and brainstem.