[Neurophysiological studies of minamata disease with HTLV-I associated myelopathy--a case report]

In both Minamata disease (MD) and HTLV-I associated myelopathy (HAM), sensory disturbance is one of the most characteristic clinical symptoms. We have examined median nerve SSEPs (MN-SEP) and posterior tibial nerve SEPs (PTN-SEP) of both patient groups, and reported their specific abnormalities. MN-SEP of MD patients never showed any conduction delay nor conduction block at the cervical cord. However, they demonstrated the initial positive cortical response with low amplitude instead of the initial negative response (N20) seen in healthy subjects. In PTN-SEP, MD patients showed the initial positive cortical response with significantly shorter latency and lower amplitude than healthy subjects. These findings have never been seen in any other diseases. On the other hand, the conduction delay and conduction block on peripheral nerve, spinal cord and/or intracranial sensory tracts have been demonstrated in many cases with HAM. The patient was a 60-year-old man. About 40 years ago, he suffered with typical clinical symptoms of MD such as cerebellar ataxia, intention tremor and sensory disturbance of upper and lower extremities, and then his condition was complicated with progressive spastic paraplegia and urinary bladder dysfunction since 30 years ago. Both MN-SEP and PTN-SEP were studied so that we could make the electrophysiological differential diagnosis of MD and HAM. His MN-SEP indicated both the conduction delay at his cervical cord and intracranial sensory tract and the initial positive potential from cephalic recording. Furthermore, his PTN-SEP demonstrated severe conduction block at the spinal cord and neither cervical response (N28) nor cortical response (P37) was evoked. In conclusion, the clinical electrophysiologic studies supported our notion that the case might be affected with both MD and HAM.