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

Objective. To 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. Methods. We studied consecutive patients referred for the clinical suspicion of OM. Patients underwent IPT and stimulated SF-EMG on the orbicularis oculi muscle. ROC curve analysis was performed to determine the accuracy of IPT, SF-EMG and their combination. Results. We included 155 patients, 102 OM and 53 with other diagnosis (OD). The IPT had a sensitivity of 86% (95%C.I. 79-93) and a specificity of 79% (95%C.I. 68-90). SF-EMG showed a sensitivity of 94% (95%C.I. 89-98) and a specificity of 79%(95%C.I. 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%C.I. 95-100) reducing the specificity to 66% (95%C.I. 53-78) whereas using the positivity of both tests we obtained a sensitivity of 82% (95%C.I. 75-90) and a specificity of 92% (95%C.I. 85-99). The negativity of both tests had a 94% (95%C.I. 87-100) negative predictive value. Comparison of the AUCs showed no differences in the diagnostic accuracy of IPT, SF-EMG and their combinations. Conclusions. IPT and SF-EMG have a similar diagnostic accuracy in patients with OM presenting with ptosis. The negativity of both tests strongly suggests another diagnosis. Classification of Evidence: This study provides Class I evidence that both the ice-pack test and single fiber EMG accurately identify patients with OM.