Comparative diagnostic yield of median and ulnar nerve repetitive nerve stimulation in generalized myasthenia gravis

Abstract

Background & Objective: Ulnar nerve repetitive nerve stimulation (RNS) is widely used in the electrophysiological evaluation of myasthenia gravis (MG), but its limited diagnostic sensitivity remains a challenge. This study aimed to directly compare the diagnostic sensitivity of low-frequency (3 Hz) median and ulnar nerve RNS in generalized MG patients positive for acetylcholine receptor (AChR) or muscle-specific kinase (MuSK) antibodies.

Methods: In this retrospective single-center study, 35 patients diagnosed with generalized MG and seropositive for AChR or MuSK antibodies were evaluated. All underwent both median and ulnar nerve RNS testing. Electrophysiological recordings were obtained from the abductor pollicis brevis (APB) muscle for the median nerve and the abductor digiti minimi (ADM) muscle for the ulnar nerve.

Results: Abnormal decremental responses were more frequent in median nerve RNS than in ulnar nerve RNS, especially among newly diagnosed patients and those with higher AChR antibody levels, although this difference was not statistically significant. Importantly, the mean decrement magnitude was significantly greater in the median nerve compared to the ulnar nerve (17.1% vs. 9.4%; p = 0.018). This difference was particularly notable in patients with mild MG symptoms (MGFA class II and III).

Conclusion: Median nerve RNS showed higher sensitivity and greater decrement magnitude than ulnar nerve RNS, particularly in mild generalized MG cases. These findings suggest that median nerve RNS is a valuable complementary diagnostic tool in MG, especially during early disease stages.