What are the benefits of single-fiber electromyography (SFEMG) in the evaluation of myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Examination of a weak muscle with SFEMG is more useful than examination with RNS in demonstrating abnormal neuromuscular transmission. SFEMG of the extensor digiti communis (EDC) yields abnormal results in 87% of patients with generalized MG. Examination of a second muscle raises the sensitivity to 99%. In ocular MG, examination of the frontalis is more useful than examination of the EDC. Frontalis findings are abnormal in almost 100% of patients, but only about 60% of EDC findings are abnormal.

Treatment with AChR inhibitors does not normalize SFEMG results. SFEMG findings are abnormal in almost 100% of patients, whereas RNS findings are abnormal in only 44-65%. SFEMG is a good substitute for RNS in patients with ocular MG; a study by Padua et al on 86 patients with ocular MG showed 100% sensitivity. [4] However, SFEMG is technically demanding and highly operator-dependent. In addition, it has a lower specificity, and it can give positive results in other neuromuscular disorders.


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