Central nervous system changes in mitochondrial encephalomyopathy: light and electron microscopic study.

An autopsy case of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is reported. It presented with generalized muscle atrophy, stroke-like episodes, schizophrenia-like mental disorder and progressive dementia. Serum lactate and pyruvate levels were high. In the biopsied muscles, ragged-red fibers were observed by light microscopy and aggregation of abnormal mitochondria with paracrystaline formation by electron microscopy. The most characteristic neuropathological findings were infarct-like lesions widespread in the cerebral cortex. In addition, this case showed some unusual pathological features: (1) diffuse moderate fibrillary gliosis in the whole cerebral and cerebellar white matter, which might have been due to metabolic disturbances; (2) several focal lesions with demyelination and numerous spheroids in the pontocerebellar fibers; and (3) marked degeneration of the posterior columns and spinocerebellar tracts. Electron microscopic examination revealed that abnormal mitochondria were markedly aggregated in smooth muscle cells and endothelium of the cerebral and cerebellar blood vessels. These fine structural findings suggest a "mitochondrial angiopathy".