Pathology of Minamata disease

Minamata disease, or methylmercury poisoning, was first discovered in 1956 around Minamata Bay, Kumamoto Prefecture, Japan. A similar epidemic occurred in 1965 along the Agano River, Niigata Prefecture, Japan. The neuropathology of Minamata disease has been well studied; this review focuses on human cases of Minamata disease in Kumamoto Prefecture. Nervous system lesions associated with Minamata disease have a characteristic distribution. In the cerebral cortex, the calcarine cortex was found to be involved in all cases of Minamata disease, particularly along the calcarine fissure. The destruction of nerve tissue was prominent in the anterior portions of the calcarine cortex. Occasionally, the centrifugal route from the visual and visual association areas (internal sagittal stratum) showed secondary degeneration in prolonged cases after acute onset. Postcentral, precentral, and temporal transverse cortices showed similar changes, though they were less severe. Intense lesions in the precentral cortex caused the development of secondary bilateral degeneration of the pyramidal tracts. In the cerebellum, the lesions occurred deeper in the hemisphere. The granule cell population was most affected. In the peripheral nerves, sensory nerves were more affected than motor nerves. Secondary degeneration of Goll's tracts was occasionally seen in prolonged or chronic cases.