Use of SEPs to localize degeneration in a rare polyneuropathy: studies on polyneuropathy associated with pigmentation, hypertrichosis, edema, and plasma cell dyscrasia.

Peripheral and cental nerve conduction were studied in five patients who had polyneuropathy associated with pigmentation, hypertrichosis, edema, and plasma cell dyscrasia by using the short-latency somatosensory evoked potential (SEP) to electrical stimulation of the median nerve at the wrist. The clavicular component N9 was markedly reduced in amplitude, and its latency was moderately prolonged. The interpeak latency from N9 to the cervical component N13 was significantly prolonged, indicating a conduction delay in the dorsal root. The interpeak latency from N13 to the cortical component N20 was normal, suggesting normal central conduction. These physiological findings were consistent with the pathological findings, which showed degeneration of axons and segmental demyelination and remyelination in the sural nerve and extensive segmental demyelination and remyelination in the dorsal root but normal posterior columns of the spinal cord. SEP is a noninvasive method of localizing the site of axon or myelin disorder in a peripheral neuropathy.