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.

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Keywords compound muscle action potential amplitude, increment, Lambert-Eaton myasthenic syndrome, repetitive nerve stimulation, sensitivity, specificity
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Journal Muscle & Nerve
Lipka, A.F. (Alexander F.), Titulaer, M.J, Tannemaat, M.R. (Martijn R.), & Verschuuren, J.J. (2020). Lowering the cutoff value for increment increases the sensitivity for the diagnosis of Lambert-Eaton myasthenic syndrome. Muscle & Nerve. doi:10.1002/mus.26885