Direct comparison of median and ulnar repetitive nerve stimulation in generalized myasthenia gravis

Abstract

Ulnar nerve repetitive nerve stimulation (RNS) has been traditionally used in the electrophysiological evaluation of myasthenia gravis (MG). However, its low diagnostic sensitivity remains a limitation. Existing data may suggest that median nerve RNS outperforms that of the ulnar nerve, but a direct comparison is currently lacking. The aim of this study was to directly compare the diagnostic yields between median and ulnar nerve RNS in patients with generalized MG. We performed a retrospective analysis of patients with MG who underwent median and ulnar nerve RNS at a single tertiary center. RNS studies of median nerve recording from the abductor pollicis brevis and ulnar nerve recording from the adductor digiti minimi were completed in 28 patients with generalized MG. Abnormal RNS was more frequently observed in the median compared with the ulnar nerve (60.7% vs 35.7%, P=.046). The average magnitude of decrement was higher in the median nerve compared with the ulnar nerve (17.3% vs 9.6%, P=.017). Differences between the median and ulnar nerve RNS studies were restricted to patients with mild manifestations (Myasthenia Gravis Foundation of America class II). Median nerve RNS has superior diagnostic sensitivity as compared with ulnar nerve RNS in the assessment of mild generalized MG.