Visual evoked responses in hereditary motor and sensory neuropathies.

The P2 latency of the pattern reversal visual evoked response was measured in 11 patients with hereditary motor and sensory neuropathy (HMSN). The P2 latency was inversely related to the peripheral nerve conduction velocity, but no significant relation was found between the P2 latency and the age of the patients or the duration of their symptoms. When the whole group was considered the mean P2 latency was longer but not significantly different from a control group. When the 11 patients were differentiated into HMSN I (5 males) and HMSN II (2 females, 4 males) the P2 latencies of the patients with HMSN I were significantly longer than those with HMSN II. The data support earlier findings that subclinical involvement of the optic nerve may occur in HMSN and suggest that measurement of P2 latency may be of value in the differentiation of HMSN. More than two subtypes, however, may exist.