Late changes in human sural nerves in Minamata disease and in nerves of rats with experimental organic mercury poisoning.

The sural nerves of 2 human cases with Minamata disease and poisoned rats were examined histopathologically. Both showed similar findings: the myelinated nerve fibres were decreased in number, but small myelinated nerve fibres were increased: The latter were irregular in shape and their Schwann cells showed regressive changes, with high electron density of the cytoplasms and many glycogen granules. Onion, bulb formation was not found. According to fibre diameter histograms, the ratio of small myelinated nerve fibres of 2–5 μm showed a high percentage. A large number of the small myelinated nerve fibres were presumed to be regenerated nerve fibres. These findings are different from other peripheral neuropathies and may be characteristics of the late changes of the sural nerve induced by organic mercury compound.