Features of central and peripheral nerve conduction in demyelinating diseases and specific neuropathies in Japan

Short latency SEPs, either with median nerve stimulation at the wrist or with tibial nerve stimulation at the ankle, were recorded in 14 patients with localized subcortical lesions, 27 Japanese patients with multiple sclerosis (MS), 5 patients each of "polyneuropathy with pigmentation, oedema, hypertrichosis and plasma cell dyscrasia (polyneuropathy with PEHP)" and subacute myelo-optico-neuropathy (SMON), and healthy adults for controls. The component N13 with median nerve stimulation was localized at C4 to C7 electrodes, and was absent in cases with cervical cord lesions but present in cases with lesions anywhere in the medulla or above. N13 was concluded to be generated in the cervical cord. Short latency SEP was found applicable to clinical investigation of the peripheral and central conduction. It was found useful for detecting subclinical demyelinating lesion in MS, and this was especially so with tibial nerve stimulation. In "polyneuropathy with PEHP," the present physiological findings (prolonged interpeak latency from N9 to N13, and amplitude reduction and delayed peak latency of N9 with median nerve stimulation) were in conformity with neuropathological findings consisting of an extensive segmental demyelination in the spinal root, and axonal degeneration and segmental demyelination in the peripheral nerve. In SMON, the primary involvement of the central conduction, exclusively in the distal portion of the gracile fasciculus, was substantiated by the present physiological findings (prolonged interpeak latency from N20 to P40 with tibial nerve stimulation, but normal SEP with median nerve stimulation).