2025 Workshop Handout Bundle-W114RFA SFEMG for NM Junction Disorders

W114RFA SFEMG for NM Junction Disorders - Sakonju Verma

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This document focuses on the use of stimulated single fiber electromyography (stimulated jitter analysis, stim-JA) of the orbicularis oculi (OO) muscle to evaluate neuromuscular junction (NMJ) disorders in pediatric and sedated patients. Traditional jitter measurement with concentric needle electrodes (CNE) demands voluntary muscle activation, difficult for children. Stim-JA using electrical stimulation overcomes this by eliciting action potentials for jitter analysis without requiring patient effort, making it more practical in infants and young children.<br /><br />The procedure involves placing a stimulating monopolar electrode above the zygomatic arch to activate the OO muscle, confirmed by muscle twitch at 3 Hz, followed by recording apparent single fiber action potentials (ASFAPs) from the OO muscle using a 25 mm CNE at 10 Hz stimulation. Recordings are analyzed for jitter—the variability in consecutive activation intervals—quantified by mean consecutive difference (MCD). The study details electrode placement, stimulation parameters, potential pitfalls, and interpretation criteria.<br /><br />Normative data show upper MCD limits in children over 2 years at 39 µs for individual fibers and 24 µs for mean MCD; values above indicate NMJ abnormalities. A model case of a 5-year-old with congenital myasthenic syndrome showed markedly increased jitter and blocking (mean MCD 69 µs, normal < 24 µs), confirming NMJ transmission defect.<br /><br />Stim-JA offers real-time, sensitive electrodiagnostic confirmation of NMJ disorders, enabling early diagnosis and treatment monitoring. Serial stim-JA measurements correlate with clinical severity and treatment response in myasthenia gravis and congenital myasthenic syndromes, supporting its role as a neurophysiological biomarker. The authors advocate stim-JA as an effective, well-tolerated method for pediatric NMJ disorder evaluation, improving diagnostic accuracy and patient care in a challenging population.<br /><br />References underscore the foundational research validating stimulated jitter analysis, technical considerations, normative values, and clinical applications in pediatric neuromuscular diseases.

Keywords

stimulated single fiber electromyography

stimulated jitter analysis

orbicularis oculi muscle

neuromuscular junction disorders

pediatric neurology

concentric needle electrodes

mean consecutive difference

congenital myasthenic syndrome

myasthenia gravis

electrodiagnostic biomarker