Longitudinal conduction studies in hereditary motor and sensory neuropathy type 1.

Motor conduction studies were performed serially in 10 patients, ages 10-62 years, with clinical and electrophysiological criteria of hereditary motor and sensory neuropathy type 1 (HMSN-1) over periods of 11-19 years. Median nerve conduction velocity (MNCV) and distal motor latency showed no significant change on serial studies. Mean median compound muscle action potential (CMAP) amplitude values, however, decreased 66% in 8 patients. Observed clinical progression in HMSN-1, over prolonged periods of time, was not associated with MNCV slowing. However, CMAP amplitude reduction, reflecting progressive axonal loss, correlated with clinical deterioration.