2023 Workshop Handout Bundle-SFEMG and Measuring Jitter Using Concentric Needle

SFEMG and Measuring Jitter Using Concentric Needle

Pdf Summary

Single Fiber Electromyography (SFEMG) is a highly selective technique for recording and analyzing electrical activity from individual muscle fibers. Developed by Dr. Donald B. Sanders and colleagues, this method allows for detailed assessment of motor unit properties, particularly fiber density (FD) and neuromuscular jitter.<br /><br /><strong>Fiber Density</strong>:<br />FD measures the number of time-locked action potentials (APs) within a specific recording area (300 µm of the SF electrode). A higher FD indicates a greater local concentration of muscle fibers, often seen in neuropathies and some myopathies as a result of muscle fiber reorganization. Measurements are taken by positioning the electrode to record APs with a maximum amplitude and counting APs in several sites within the muscle. Normative FD values vary with muscle type and age.<br /><br /><strong>Neuromuscular Jitter</strong>:<br />Jitter refers to the variability in time from nerve stimulus to AP response, indicative of neuromuscular transmission safety. It is measured during either axonal stimulation or voluntary muscle activation. For axonal stimulation, the motor nerve is stimulated, and jitter is calculated by analyzing APs from muscle fibers in response to the stimulus. High jitter suggests impaired neuromuscular transmission, common in myasthenia gravis and other neuromuscular disorders.<br /><br /><strong>Jitter Measurement Techniques</strong>:<br />- <strong>Axonal Stimulation</strong>: Useful when patient cooperation is limited. It involves stimulating the motor nerve and recording responses from muscle fibers.<br />- <strong>Voluntary Activation</strong>: Requires patient cooperation to slightly contract the muscle, with jitter measured between pairs of APs from the same motor unit.<br /><br /><strong>Applications</strong>:<br />- <strong>Myasthenia Gravis (MG)</strong>: SFEMG detects increased jitter in virtually all MG patients, even in muscles with normal strength.<br />- <strong>Lambert-Eaton Myasthenic Syndrome (LEM)</strong>: Characterized by increased jitter and frequent impulse blocking.<br />- <strong>Neuropathies and Myopathies</strong>: SFEMG reveals increased jitter and rearrangement of muscle fibers, offering insights into the ongoing processes of denervation and reinnervation.<br /><br /><strong>Concentric Needle (CN) Electrodes</strong>:<br />By adjusting filter settings, CN electrodes can approximate single fiber APs, termed "apparent single fiber action potentials" (ASFAPs). They offer a less invasive means to measure jitter, albeit with some limitations compared to true SFEMG.<br /><br />References and guidelines set forth by SFEMG experts provide protocols to ensure accurate jitter analysis, emphasizing the need for experience and precision in technique. SFEMG uniquely contributes to the understanding and diagnosis of various neuromuscular diseases.

Keywords

Single Fiber Electromyography

SFEMG

Fiber Density

Neuromuscular Jitter

Axonal Stimulation

Voluntary Activation

Myasthenia Gravis

Lambert-Eaton Myasthenic Syndrome

Neuropathies

Concentric Needle Electrodes