Electrophysiological features of hirayama disease

The purpose of this study was to compare the pattern of hand muscle involvement in Hirayama disease (HD) and amyotrophic lateral sclerosis (ALS).We reviewed findings of upper limb nerve conduction studies of 46 HD patients and 60 ALS patients. The findings from 54 healthy subjects were used for comparison.In HD, the ulnar compound muscle action potential (CMAP) amplitude was more severely reduced than the median one, and the reverse pattern was observed in ALS. The mean ulnar/median (U/M) CMAP amplitude ratio was significantly lower in HD (0.64 ± 0.79) and abnormally higher in ALS (2.15 ± 1.77) compared with normal subjects (0.89 ± 0.23). An abnormally low U/M CMAP amplitude ratio (<0.6) was encountered in 34 patients with HD and in 1 with ALS. A U/M CMAP amplitude ratio ≥4.5 or absent median motor response was found only in ALS.Our findings demonstrate different patterns of hand muscle involvement between these two diseases.