Post-exercise exhaustion in Lambert-Eaton myasthenic syndrome

Abstract Objectives To study post-exercise exhaustion by decrement (PEE-D) systematically in 24 repetitive nerve stimulation (RNS) tests in 14 patients with Lambert–Eaton myasthenic syndrome (LEMS). Methods In the abductor digiti quinti muscle, the compound muscle action potential (CMAP) amplitude and 3 Hz responses for 2 s were obtained with the supramaximal stimulation at rest, immediately after (PE0), 30 s after (PE30s), and at 1, 2, 3, and 4 m after 10-s exercise. Results There was a 377% increment in the CMAP amplitude at PE0 and a mild increment (+26%) at PE30s. A transient but significant improvement (−22%) in the decremental response was observed at PE0, and a gradual worsening of decrement in subsequent tests, with the worst decrement noted (−50%) at PE2m. Conclusion PEE-D was found 2 m after exercise in LEMS. Significance PEE-D may be physiologically closest to the reversible myasthenic fatigue after exercise observed in LEMS patients.