ELECTROPHYSIOLOGICAL FEATURES OF HIRAYAMA DISEASE

Introduction: The purpose of this study was to compare the pattern of hand muscle involvement in Hirayama disease (HD) and amyotrophic lateral sclerosis (ALS). Methods: 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. Results: 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. Conclusion: Our findings demonstrate different patterns of hand muscle involvement between these two diseases. Muscle Nerve 44: 185-190, 2011