Biopsy of the sural nerve was performed on three patients with severe Minamata disease of more than 10 years duration. There
were so many unmyelinated and poorly myelinated nerve fibers that myelinated fibers scattered irregularly in small numbers
or in groups of peculiar features in the intraneural bundle. Abnormaly thin or poorly formed myelin sheaths were noticed.
Incomplete myelination and abnormal myelination varied in size and shape appeared as fetal anomaly. Regenerated axons extremely
small in size remained singly or in groups following regenerative sprouting. Sometimes, extremely small axons with normal
myelination were noticeable, while the axons were lost, leaving myelin sheaths. Axons occasionally contained increased neurofilaments.
Schwann cells were not so increased as in adult Minamata disease.
Degenerative changes of nerve fibers still proceeded, presumably because the patients lived in the mercury-contaminated district.
Myelin degenerations and glycogen deposits in the axoplasm were identified.
Key words Intrauterine poisoning - Methylmercuric neuropathy - Sural nerve biopsy - Myelination anomaly
This work was supported by a Grant-in-Aid for Scientific Research, Ministry of Education, Science, and Culture, Japan (No.
848096)