What are the clinical applications of 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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Single-fiber electromyography (SFEMG) is most valuable clinically in the patient with suspected myasthenia gravis (MG) in whom results of other tests of neuromuscular transmission and acetylcholine receptor (AChR) antibody measurements are normal. [1, 10]  FEMG is also helpful in estimating the fiber density, which assesses the focal organization of the motor unit.

Some studies looked at the prognostic utility of SFEMG in terms of identifying patients with ocular myasthenia gravis, but they were not conclusive. One study found that increased jitter value in orbicularis oculi muscles correlated with increased disease exacerbations. [11] SFEMG can also be used in the setting of other disorders of neuromuscular transmission like Lambert Eaton myasthenic syndrome (LEMS) and botulism. Jitter is markedly increased in LEMS, frequently being out of proportion to the severity of weakness with frequent impulse blocking. In motor neuron disease, jitter, fiber density, or both are increased in 70% of muscles in which no other abnormality could be detected by routine EMG. [12]  

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