Lowering the Cutoff Value for Increment Increases the Sensitivity for the Diagnosis of Lambert‐Eaton Myasthenic Syndrome

BACKGROUND:Increment of compound muscle action potential amplitude is a diagnostic hallmark of Lambert-Eaton myasthenic syndrome (LEMS). Making a diagnosis can be challenging, therefore, a proper cutoff for abnormal increment is highly relevant for improved recognition of this rare disease.METHODS:We determined the sensitivity and specificity of 60% and 100% cutoff values in all consecutive patients who underwent increment testing in our hospital from 1999 to 2016.RESULTS:We included 156 patients, 63 with LEMS and 93 without LEMS. Sensitivity of a 60% cutoff for increment testing was 77.8% (95% confidence interval 65.5%-87.3%) and 58.7% (45.6%-71.0%) for 100%. Specificity was 98.9% (94.2%-100%) and 100% (96.1%-100%) using a threshold of 60% and 100%, respectively.CONCLUSIONS:Lowering the cutoff value for abnormal increment to 60% greatly increases sensitivity to diagnose LEMS without an overt loss in specificity.