An electrophysiological study of Hirayama disease

Abstract

Objective To analyze the electrophysiological characteristics of Hirayama disease and explore their significance for its diagnosis. Methods Electrophysiological tests were performed on 18 patients who fulfilled the clinical criteria for Hirayama disease. Sixteen were males and 2 were females. The mean age was 24.9years old ( 19-58 years), and the mean case history was 5.2 years ( 1-40 years). The Hirayama disease was clearly unilateral in 10 patients and bilateral in 3, with 5 cases suspected of being bilateral. Motor neuron conduction velocity (MCV) and sensory neuron conduction velocity (SCV) were measured in the median and ulnar nerves.Electromyograms (EMGs) of the abductor digiti minimi, abductor pollicis brevis, extensor digitorum communis,brachioradialis muscle, biceps brachii and sternocleidomastoid were recorded in all cases. The MCV and SCV of the common peroneal nerve and an EMG of the tibialis anterior muscle were examined in one leg. The MCV and SCV of the ulnar nerve and EMGs of the abductor digiti minimi, extensor digitorum communis and brachioradialis muscles were inspected on the contralateral sides of 8 cases, including the patients suspected of suffering bilateral Hirayama disease. The MCVs of the median and ulnar nerves were examined segmentally by stimulating the nerves distally as well as proximally, and recording the amplitude, duration and area of compound muscle action potentials (CMAP) and changes in wave form, then determining whether there was a nerve conduction block. Results (1) No conduction block was detected in any median nerve or ulnar nerve among the 18 cases. (2) All the SCVs and sensory nerve action potentials of the median and ulnar nerves were normal. ( 3 ) All the MCVs and SCVs of the common peroneal nerve and the EMGs of the anterior tibialis muscles were normal. (4) MCV slowing in the upper limbs accounted for 41.3％ (19/44) of the examined nerves. The rates of MCV decrease were 72.2％ (13/18)in the ulnar nerve on the affected sides, 33.3％ (6/18) in the median nerve on the affected sides and 0％ (0/8)in the ulnar nerve on the contralateral sides. (5) Amplitude reduction in the CMAP in the upper limbs accounted for 81.8％ (36/44) of the examined nerves. The rates of amplitude decrease were 100％ (18/18) in the ulnar nerves of the affected sides, 77.8％ (14/18) of median nerves on the affected side and 50％ (4/8) of ulnar nerves on the contralateral side. ( 6 ) Upper limb EMGs revealed a rate of neurogenic damage of 47.0％ ( 62/132). The EMGs decreased in 100％ (18/18) of the abductor digiti minimi and abductor pollicis brevis on the affected side, 88.9％ (16/18) of extensor digitorum communis on the affected side, 62.5％ (5/8) of the abductor digiti minimi on the contralateral side, 37.5％ (3/8) of the extensor digitorum communis on the contralateral side,5.6％ ( 1/18 ) of the brachioradialis and biceps brachii muscles on the affected sides. There was no neurogenic damage of the contralateral brachioradialis muscle or the sternocleidomastoid on the affected side. Conclusions The electrophysiological features of Hirayama disease include unilateral or bilateral neurogenic damage in the upper limbs. According to the abnormal EMGs, spinal anterior horn cells on the affected sides were injured at C7-T1. C6and above C6 were rarely involved. The electrophysiological characteristics of Hirayama disease could provide a clear basis for localization and differentiation in Hirayama disease diagnosis. Key words: Hirayama disease; Electrophysiology