Reliability of SFEMG in diagnosing myasthenia gravis: sensitivity and specificity calculated on 100 prospective cases

Clin Neurophysiol. 2014 Jun;125(6):1270-3. doi: 10.1016/j.clinph.2013.11.005. Epub 2013 Nov 15.


Objective: The study aimed to determine the utility of single-fibre electromyography (SFEMG) in the diagnosis of myasthenia gravis (MG) in subjects with a clinical suspicion of the disease.

Methods: We performed a prospective, single-blinded study on 100 consecutive patients. SFEMG was not considered a criterion in making the MG diagnosis. For all cases, a different physician than the one performing SFEMG made the diagnosis of MG. All subjects underwent standard SFEMG of a single muscle, the orbicularis oculi.

Results: SFEMG was abnormal in 67 of 100 patients. A final diagnosis of definite MG was made in 54 patients (30 men/24 women). SFEMG was positive in 53 of 54 patients diagnosed with MG. The sensitivity of SFEMG in diagnosing MG was 98% (95% CI: 0.94-1.02), while the specificity was 70% (95% CI: 0.54-0.86), with a positive predictive value of 79% (95% CI: 0.74-0.79) and a negative predictive value of 97% (95% CI: 0.94-0.99).

Conclusions: In this cohort of patients, normal SFEMG findings were unlikely to occur in patients with MG.

Significance: SFEMG is not a confirmatory test for the diagnosis of MG, but it has a high negative predictive value in identifying patients without MG.

Keywords: Myasthenia gravis; Neuromuscular transmission; Single-fibre electromyography.

Publication types

  • Clinical Trial

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Blinking / physiology
  • Cohort Studies
  • Electromyography*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Myasthenia Gravis / diagnosis*
  • Predictive Value of Tests
  • Prospective Studies
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Single-Blind Method
  • Young Adult