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

Abstract

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