Assessment of the compound muscle action potential amplitude return time between exercises or tests in the repetitive nerve stimulation test for Lambert-Eaton myasthenic syndrome.

INTRODUCTION: When performing postexercise facilitation (PEF) as part of the repetitive nerve stimulation (RNS) test in Lambert-Eaton myasthenic syndrome (LEMS), it is important to avoid any influence of the previous exercise or RNS test on the compound muscle action potential (CMAP) amplitude.

METHODS: To measure the CMAP amplitude return time (ART) to that at rest, a single CMAP was obtained every 30 seconds until the amplitude was within 5% of that at rest in three exercise periods (10, 20, and 30 seconds) and in 10-second postexercise (PE) 3-Hz RNS testing with 17 tests in 10 LEMS patients.

RESULTS: Adequate ART between tests is 150 seconds for 10-second exercise (Ex) and 10-second PE 3-Hz RNS test, 120 seconds for 20-second Ex, and 90 seconds for 30-second Ex.

DISCUSSION: We recommend 150 seconds as adequate ART between the PEF test and the next test when performing RNS test in LEMS.