What is neuromuscular jitter in single-fiber electromyography (SFEMG)?

Updated: Mar 13, 2019
  • Author: Pradeep C Bollu, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
  • Print


When APs elicited by nerve stimulation are recorded with an SFEMG electrode, the latency from stimulus to response varies (see image below). This variation is the neuromuscular jitter, most of which is produced by fluctuations in the time for endplate potentials at the neuromuscular junction to reach the AP threshold. [15]

Electrode setup for single-fiber electromyography Electrode setup for single-fiber electromyography (SFEMG) during intramuscular axonal stimulation. The stimulating electrode is inserted into the muscle near an intramuscular nerve fiber, and the recording electrode is inserted distally near muscle fibers innervated by this nerve. During repetitive stimulation of the nerve, the latency between stimulus and action potentials (APs) varies among successive responses (ie, the neuromuscular jitter).

When the SFEMG electrode is positioned to record from 2 or more muscle fibers in one voluntarily activated motor unit, the neuromuscular jitter is seen as variations in the time intervals between pairs of APs from these fibers (see images below). This paired jitter represents the combined jitter in 2 endplates.

Recording position of the single-fiber electromyog Recording position of the single-fiber electromyography electrode during jitter analysis with voluntary muscle activation. The electrode is positioned to record action potentials (APs) from 2 muscle fibers that are innervated by the same motor nerve fiber.
Single-fiber electromyography. Action potentials r Single-fiber electromyography. Action potentials recorded from 2 muscle fibers with normal jitter during voluntary muscle activation. Ten consecutive discharges are superimposed. The oscilloscope is triggered by the rising portion of the first potential, which falls at the same position with each discharge. The second potential falls at slightly varying positions among successive discharges, demonstrating the neuromuscular jitter.

Jitter may be measured either as the nerve is stimulated or as the patient voluntarily activates the muscle.

Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!