2024 Workshop Handout Bundle-W07C SFEMG Sanders

W07C SFEMG Sanders

Pdf Summary

Single Fiber Electromyography (SFEMG), introduced by Dr. Donald B. Sanders, is a highly selective electromyography (EMG) technique designed to record action potentials (APs) from individual muscle fibers. Its selectivity is due to a small recording surface (25 µm diameter) on the electrode and the use of a high-pass filter of 500 Hz. SFEMG allows for the unique measurement of two key features in the motor unit: fiber density (FD) and neuromuscular jitter.<br /><br />Fiber density measurements indicate the local concentration of muscle fibers within a motor unit, essential for detecting neuropathies and some myopathies. This is done by recording APs with amplitudes greater than 200 µV from different sites in the muscle. The FD increases with age and chronic muscle use, especially marked in distal muscles.<br /><br />Neuromuscular jitter refers to the variability in latency between nerve stimulus and muscle response, reflecting the safety factor of neuromuscular transmission. This can be measured during voluntary muscle activation or axonal stimulation, each providing specific diagnostic insights. Jitter increases in conditions like myasthenia gravis (MG), where it can be recorded with consistent repetitive nerve stimulation.<br /><br />SFEMG is particularly sensitive, helping diagnose disorders such as MG, Lambert-Eaton Myasthenic Syndrome (LEM), neuropathies, and myopathies. Abnormalities detected via SFEMG include increased jitter and blocking, which signify inefficient neuromuscular transmission. SFEMG findings in myopathies reveal fiber reinnervation, grouping, and splitting, indicating muscle pathology.<br /><br />In clinical practice, care must be taken to assure high-quality signal acquisition and precise jitter measurement. This requires significant experience and careful technique. Guidelines suggested by various experts and organizations, including criteria for signal quality and electrode use, have standardized SFEMG measurements, improving diagnostic accuracy and reliability. Normative values and practice recommendations ensure that SFEMG remains an invaluable tool for diagnosing neuromuscular disorders.

Keywords

Single Fiber Electromyography

SFEMG

action potentials

fiber density

neuromuscular jitter

neuromuscular disorders

myasthenia gravis

electrode

diagnostic accuracy

muscle pathology