Comparison of ice pack test and single-fiber EMG diagnostic accuracy in patients referred for myasthenic ptosis

Abstract

ObjectiveTo compare the diagnostic accuracy of ice pack test (IPT) and single-fiber EMG (SF-EMG) in patients with suspected ocular myasthenia (OM) presenting with ptosis.MethodsWe studied consecutive patients referred for the clinical suspicion of OM. Patients underwent IPT and stimulated SF-EMG on the orbicularis oculi muscle. Receiver operating characteristic curve analysis was performed to determine the accuracy of IPT, SF-EMG, and their combination.ResultsWe included 155 patients, 102 with OM and 53 with other diagnosis (OD). The IPT had a sensitivity of 86% (95% confidence interval [CI] 79–93) and a specificity of 79% (95% CI 68–90). SF-EMG showed a sensitivity of 94% (95% CI 89–98) and a specificity of 79% (95% CI 68–90). Overall, IPT and SF-EMG showed discordant results in 30 cases, 16 OM and 14 OD. The combination of IPT and SF-EMG, using the positivity of at least one test for OM diagnosis, increased the sensitivity to 98% (95% CI 95–100), reducing the specificity to 66% (95% CI 53–78), whereas using the positivity of both tests, we obtained a sensitivity of 82% (95% CI 75–90) and a specificity of 92% (95% CI 85–99). The negativity of both tests had a 94% (95% CI 87–100) negative predictive value. Comparison of the areas under the curve showed no differences in the diagnostic accuracy of IPT, SF-EMG, and their combinations.ConclusionsIPT and SF-EMG have similar diagnostic accuracy in patients with OM presenting with ptosis. The negativity of both tests strongly suggests another diagnosis.Classification of evidenceThis study provides Class I evidence that both the IPT and SF-EMG accurately identify patients with OM.