The electrophysiological profile of hereditary motor and sensory neuropathy-Lom.

OBJECTIVE To make electrophysiological observations on a large kindred with hereditary motor and sensory neuropathy-Lom (HMSN-L) containing 27 affected individuals. CLINICAL FINDINGS Onset was in early childhood with gait difficulty related to progressive lower limb weakness. Upper limb weakness developed later. Bulbar involvement was present in one third of the patients, and deafness appeared during the second or third decades. ELECTROPHYSIOLOGICAL FINDINGS: Electromyographic evidence of denervation was progressive, more severe distally, and greater in the legs, being total in distal lower limb muscles in most patients. Sensory action potentials were absent and motor nerve conduction was severely slowed. This included proximal upper limb (musculocutaneous and axillary), hypoglossal, and facial nerves. The severity of slowing increased during childhood. M waves, often multiple, were recorded in all affected individuals. The blink reflex showed an unusual three component response. The latencies of all three components were prolonged. CONCLUSIONS HMSN-L is shown to be a demyelinating neuropathy involving severe and early axonal loss. The progressive slowing of nerve conduction during childhood differs from the static reduction seen in type I HMSN.