A novel approach to the measurement of motor conduction velocity using a single fibre EMG electrode

OBJECTIVE: To evaluate whether, for patients with suspected myelin impairment, the sensitivity of motor nerve conduction studies can be increased by using an SFEMG electrode which makes it possible to study conduction velocity in a small number of axons (SF-CV). METHODS: We studied 22 consecutive patients with suspected neuropathy through conventional motor conduction study and through SF-CV. For each patient we selected a nerve that was normal at conventional neurography and studied it through SF-CV. Also, we performed SF-CV in 15 healthy subjects. We considered 36 m/s as the low limit of normal SF-CV (the normal value commonly accepted in the literature for the slowest alpha motor axons). RESULTS: In the healthy subjects we never observed abnormal SF-CV values. Of the 22 patients, in 18 the conventional tests showed abnormal findings suggestive of neuropathy. The remaining 4 patients were completely normal at the conventional tests. Through SF-CV we studied 22 nerves that were normal at the conventional tests. Fourteen of 22 (64%) nerves presented pathological SF-CV test. Half of the patients with normal findings at the conventional tests showed pathological SF-CV test. CONCLUSIONS: SF-CV evaluation may be useful in detecting early, mild, or partial myelin damage, because it makes it possible to detect nerve conduction slowing when conventional tests are normal. SIGNIFICANCE: Increasing sensitivity of motor conduction evaluation.