briefly on SFEMG: ( from: Advances in the Diagnosis of Neuromuscular Junction Disorders; Matthew N. Meriggioli, MD Donald B. Sanders, MD )
Quote:
Single-fiber electromyography (SFEMG) is a selective recording technique in which a specially constructed concentric needle electrode is used to identify and record action potentials from individual muscle fibers. Measurement of jitter by SFEMG is the most sensitive clinical test for detection of a defect in neuromuscular transmission. This sensitivity allows for demonstration of abnormalities even in clinically unaffected muscles. During sustained activation of the motor nerve, the latency from nerve activation to muscle action potential varies from discharge to discharge.
This variation is the neuromuscular jitter and is produced by fluctuations in the time it takes for the endplate potential at the NMJ to reach the threshold
for muscle action potential generation. These fluctuations are in turn due to the normally varying amount of acetylcholine released from the nerve terminal after a nerve impulse. A small amount of jitter is seen in normal muscles due to this phenomenon. An increase in the jitter is the most sensitive electrophysiologic evidence of a defect in neuromuscular transmission. When the defect is more severe, some nerve impulses fail to elicit action potentials, and SFEMG recordings demonstrate an intermittent absence of one or more single muscle fiber action potentials on consecutive
firings. This is called impulse blocking and represents neuromuscular transmission failure at the involved endplate.
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