What are jitter values in single-fiber electromyography (SFEMG)?

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

Answer

Reference jitter values have been determined for many muscles. [5, 6]

  • Jitter increases slightly with age in normal subjects.

  • A study is abnormal if the mean (or median) jitter exceeds the upper limit for the muscle, or if more than 10% of pairs or endplates have increased jitter or blocking.

Jitter less than 5 µs is seen rarely in voluntarily activated SFEMG studies in normal muscles and more often in myopathies. [7]

  • These low values probably result from recordings that are made from split muscle fibers, both branches of which are activated by a single neuromuscular junction.

  • These values should not be included in assessments of neuromuscular transmission.

The MCD value that is measured during axonal stimulation is less than that measured during voluntary activation of the same muscle; the latter comes from only single endplates. [8]

Reference values for jitter during axonal stimulation have been determined for the extensor digitorum communis (EDC) and orbicularis oculi muscles. [5, 6]

  • For other muscles, the normative values for stimulation jitter can be obtained by multiplying the values for voluntary activation by a conversion factor of 0.8. [9]

  • MCD values less than 5 µs that are obtained during stimulation SFEMG occur when the muscle fiber is stimulated directly; these values should not be used for assessing neuromuscular transmission.


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