Mixed and sensory nerve action potentials of the median nerve in patients with peripheral neuropathy or motor neurone disease.

Sensory nerve action potentials (SNAP) and mixed nerve action potentials (MNAP) of the median nerve were examined in 16 patients with motor neurone disease (MND), 29 patients with peripheral neuropathy and 18 age-matched normal controls. Patients with MND showed almost normal amplitudes of SNAP and MNAP, though they had muscle weakness in the hands. The motor nerve fibres may have a negligible effect on MNAP. The amplitude of MNAP correlated well with that of SNAP. The sensory fibres may play a major role in MNAP. Patients with peripheral neuropathy showed a significant reduction in amplitude in SNAP and MNAP. In particular, patients with sensory disturbance in the hands elicited low amplitudes in SNAP and MNAP. Patients without sensory disturbance also showed a decrease in amplitude in SNAP and MNAP. Peripheral neuropathy patients without sensory disturbance might show subclinical disturbance of peripheral sensory nerve fibres.