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

ObjectiveThe 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.MethodsWe 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.ResultsSFEMG 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).ConclusionsIn this cohort of patients, normal SFEMG findings were unlikely to occur in patients with MG.SignificanceSFEMG is not a confirmatory test for the diagnosis of MG, but it has a high negative predictive value in identifying patients without MG.