Compound Muscle Action Potential Decrement to Repetitive Nerve Stimulation Between Hirayama Disease and Amyotrophic Lateral Sclerosis.

PURPOSE: To compare repetitive nerve stimulation (RNS) between Hirayama disease (HD) and amyotrophic lateral sclerosis (ALS).

METHODS: The 3-Hz RNS test was performed on bilateral abductor pollicis brevis, abductor digiti minimi, middle deltoid, and upper trapezius muscles in 33 HD patients and 37 ALS patients.

RESULTS: In HD patients, none of tested muscles showed any abnormal decrements (≥10%). Significant decrements were observed in 73% of the ALS patients, and decrements were more frequently observed in proximal muscles (deltoid: 70.3%; trapezius: 48.6%). Illness duration did not correlate with decrement percentage in either patient group, and there was no relationship between decrement incidence and ALS diagnostic category (P > 0.05).

CONCLUSIONS: The significantly different RNS results between ALS and HD patients support the application of RNS, especially performing RNS in proximal muscles, as a supplementary test in distinguishing these two diseases, even in the early stages. These results may also imply a difference in underlying pathophysiology between ALS and HD.