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.

Abstract

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