2022 Workshop Handout Bundle-SFEMG and Measuring Jitter Using Concentric Needle- Massey Sanders

SFEMG and Measuring Jitter Using Concentric Needle- Massey Sanders

Pdf Summary

Single Fiber Electromyography (SFEMG) is a technique that allows the identification and measurement of action potentials (APs) from individual muscle fibers. SFEMG uses a small recording surface to enhance selectivity and a high pass filter to filter out low frequency components. SFEMG can measure two features of the motor unit: fiber density (FD) and neuromuscular jitter. <br /><br />Fiber Density (FD) provides information about the local concentration of muscle fibers within the motor unit. By measuring the number of time-locked APs with certain characteristics, FD can be calculated, which quantifies the density of muscle fibers within the motor unit. FD is increased in neuropathies and some myopathies. Normative values for FD have been determined for different muscles, and FD increases with age.<br /><br />Neuromuscular jitter measures the variation in latency between nerve stimulation and AP response. Jitter is increased when the safety factor of neuromuscular transmission is compromised. Jitter can be measured during axonal stimulation or voluntary muscle activation. Jitter is increased in myasthenia gravis and Lambert-Eaton myasthenia syndrome.<br /><br />SFEMG findings can be used in the assessment of various neuromuscular conditions. In neuropathies, increased FD and jitter suggest reinnervation and uncertain neuromuscular transmission. In myopathies, increased FD indicates focal grouping and abnormal neuromuscular transmission. SFEMG can also be used to mark individual motor units and measure late responses.<br /><br />Jitter can also be measured with concentric needle (CN) electrodes, although these recordings do not distinguish between single APs and superimposed APs. Reference values have been established for jitter measured with CN electrodes, but the filter settings and technique must be standardized.<br /><br />In conclusion, SFEMG is a useful technique for investigating neuromuscular conditions, providing valuable information about muscle fiber density and neuromuscular transmission. CN electrodes can also be used to measure jitter, but strict criteria and reference values should be followed.

Keywords

Single Fiber Electromyography

SFEMG

action potentials

muscle fibers

fiber density

neuromuscular jitter

neuropathies

myopathies

reinnervation

neuromuscular transmission