Electrophysiological characteristics of juvenile muscular atrophy of distal upper extremity ( Hirayama's disease)

Abstract

Objective The purpose of this study was to retrospectively evaluate the electrophysiological characteristics of Hirayama disease. Methods Electrophysiological records of 77 patients with a diagnosis of Hirayama disease were reviewed. We analyzed the amplitude of compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) as well as the F wave latency and frequency of median and ulnar nerves. We also evaluated the changes of needle electromyography. Results Of the 77 patients, 74 were male and 3 female. Mean age of onset was ( 17.7 ± 2.6 ) years and mean disease duration (28.2 ± 25.7 ) months. 57 of the 77 patients showed clinical presentation of unilateral involvement. Reduced ulnar CMAP amplitude was found prodominantly. Abnormal F wave frequency was found in the majority of the patients in both median and ulnar nerves and there was also correlation between F wave frequency and amplitude of CMAP. Sensory conduction studies were normal. In the needle EMG, neurogenic changes were found in both upper limbs in 67 cases and the remaining 10 patients were unilateral involved. Denervation was found in the C7-T1 myotomes in all of the 77 patients. Among them, 15 also showed C5, C6 involvement with different extent. Conclusion In this study, the most obvious electrophysiological abnormality was reduced F wave frequency in both median and ulnar nerves followed by reduced ulnar CMAP amplitude. Although most patients showed unilateral involvement clinically,needle EMG found 87% had bilateral neurogenic changes. Although C7, C8, T1 myotomes were mainly damaged in Hirayama disease, C5,C6 was also involved in around 1/5 of the patients. Key words: Muscular atrophy; Upper extremity; Electromyography; F wave