Exploring the Value of Quantitative Muscle Ultrasound in Neuromuscular Junction Disorders: A Pilot Study

INTRODUCTION/AIMS: Quantitative muscle ultrasound (QMUS) is a validated technique for assessing muscle pathology, yet its role in disorders primarily affecting the neuromuscular junction (NMJ) remains unclear. This pilot study aimed to explore whether QMUS is associated with structural muscle changes in patients with acquired or genetic NMJ disorders. METHODS: We conducted a retrospective study of 18 patients with confirmed NMJ disorders who underwent electrodiagnostic testing (EDx), including repetitive nerve stimulation (RNS) and/or stimulated single-fiber electromyography (SFEMG), combined with QMUS. Patients were grouped into congenital myasthenic syndromes (CMS) and acquired autoimmune myasthenia (myasthenia gravis [MG] or Lambert-Eaton myasthenic syndrome [LEMS]). QMUS scores were classified as normal, borderline, or abnormal based on muscle echogenicity z-scores derived from a validated algorithm. RESULTS: Abnormal EDx was present in 13 of 18 (72%) patients. Abnormal decrement (> 10%) was observed in 7/18 patients, and abnormal jitter in the orbicularis oculi muscle was found in 6/8 patients. QMUS demonstrated normal echogenicity in 14/18 (78%) patients, while 4/18 (22%) showed abnormal or borderline echogenicity, including 2/5 (40%) with generalized MG. All patients with borderline or abnormal QMUS findings had concomitant abnormal RNS and/or SFEMG. DISCUSSION: Structural muscle changes, reflected by altered echogenicity, may occur in a subset of patients with NMJ disorders, although QMUS shows limited sensitivity compared with EDx. Future studies using standardized protocols, dynamic assessments, and targeted evaluation of clinically relevant muscles, such as facial and bulbar, are needed to determine whether QMUS may serve as a complementary tool for disease characterization or monitoring.