Single fiber electromyography and measuring jitter with concentric needle electrodes

Abstract

This monograph contains descriptions of the single fiber electromyography (SFEMG) method and of the more recently implemented method of recording jitter with concentric needle electrodes (CNEs). SFEMG records action potentials from single muscle fibers (SFAPs), which permits measuring fiber density (FD), a sensitive measure of reinnervation, and jitter, a sensitive measure of abnormal neuromuscular transmission (NMT). With voluntary activation, jitter is measured between two SFAPs with acceptable amplitude and rise time. With activation by axon stimulation, jitter is measured between the stimulus and individual SFAPs. Pitfalls due to unstable triggers and inconstant firing rates during voluntary activation and subliminal stimulation during axon stimulation should be identified and avoided. In CNE recordings, spikes with shoulders or rising phases that are not parallel are produced by summation of SFAPS; these should be excluded and reference values for CNE jitter should be used. CNE and SFEMG have similar and very high sensitivity in detecting increased jitter, as in myasthenia gravis and other myasthenic conditions. However, jitter is also seen in ongoing reinnervation and some myopathic conditions. With SFEMG, these can be identified by increased FD; however, FD cannot be measured with CNE, and conventional electromyography should be performed in muscles with increased jitter to detect neurogenic or myogenic abnormalities. Jitter is abnormal after injections of botulinum toxin, even in muscles remote from the injection site, and can persist for 6 mo or more. This can complicate the detection or exclusion of abnormal NMT.

Muscle fiber conduction velocity in situ revisited: A new approach to an ancient technique

“…The MFAP has confirmed after 50-100 consecutive discharges a time variability (MCD) of <5 µs, similar to the number used for the neuromuscular jitter (6). However, <50 could be acceptable to confirm a direct muscle fiber stimulation.…”

“…(5) The calculated MFCV is taken from the MFAP with the shortest latency. (6) The MFAPs dots on the histogram are easily selected, eliminating the spurious array. (7) The response vs. latency graph makes distinguishing direct or indirect muscle stimulation easy.…”