2024 Workshop Handout Bundle-W31AS SFEMG and Jitter Measurement During Voluntary Muscle Contraction Punga

W31AS SFEMG and Jitter Measurement During Voluntary Muscle Contraction Punga

Pdf Summary

Single-Fiber Electromyography (SFEMG) is a highly sensitive technique for detecting neuromuscular transmission failures. It captures action potentials (APs) from individual muscle fibers within a motor unit, allowing precise detection of subclinical defects even in asymptomatic muscles. Originating in Uppsala, Sweden, SFEMG measures "jitter," the variation in timing between APs from the same motor unit. High jitter indicates transmission failure or blocking. To evaluate jitter, either voluntary muscle contraction or electrical stimulation is used.<br /><br />Reusable SFEMG electrodes from the 1960s faced restrictions, leading to the use of concentric needle electrodes (CNE) for jitter measurement. CNE recordings typically involve slightly different filtering settings compared to SFEMG electrodes, adjusting for amplitude and frequency properties.<br /><br />Muscle selection is crucial for SFEMG, with the orbicularis oculi and frontal muscles preferred for their sensitivity in detecting abnormalities in conditions like Myasthenia Gravis (MG). Key pre-examination considerations include accounting for medications, like acetylcholinesterase inhibitors, which can influence jitter results. Clear signal identification from at least two muscle fibers is essential, and fiber pair analysis involves measuring inter-potential intervals (IPIs) to detect variability, which may signal neuromuscular blocking.<br /><br />SFEMG's diagnostic role extends to various conditions, including MG, Lambert-Eaton Myasthenic Syndrome (LEMS), congenital myasthenic syndromes (CMS), and others. Despite high sensitivity (98%) for detecting neuromuscular transmission issues, its specificity is lower (70%), necessitating supplementary tests like routine nerve conduction studies.<br /><br />Practical considerations for efficiency include potentially reducing the number of fiber pairs analyzed without compromising test accuracy. Results are typically reported in terms of the percentage of abnormal fiber pairs and mean MCD values. SFEMG recordings can detect clinical nuances, even predicting treatment responses and aiding early diagnosis in acute cases. Potential pitfalls involve technical factors like ensuring clear signal sweeps, properly interpreting borderline results, and considering biological influences such as medication effects and states of denervation and reinnervation.

Keywords

Single-Fiber Electromyography

SFEMG

neuromuscular transmission

jitter

action potentials

concentric needle electrodes

Myasthenia Gravis

Lambert-Eaton Myasthenic Syndrome

muscle fibers

diagnostic sensitivity