Brainstem auditory evoked responses in hereditary motor-sensory neuropathy: site of origin of wave II.

In three patients with hereditary motor-sensory neuropathy (HMSN), type I, brainstem auditory evoked responses (BAERs) showed prolongation of the latency of all major components. Interpeak latency I-III was prolonged, but the III-V interval was normal, and separation of waves I and II accounted for the prolonged I-III interval. Prolongation of I-II interval in this condition, which affects the peripheral nerves, preservation of wave II after cerebral death, and preservation of only waves I and II in the leukodystrophies suggest that wave II may be generated in the intracranial extramedullary portion of the eighth nerve.