Post-exercise exhaustion in Lambert-Eaton myasthenic syndrome

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).

In the abductor digiti quinti muscle, the compound muscle action potential (CMAP) amplitude and 3Hz responses for 2s were obtained with the supramaximal stimulation at rest, immediately after (PE0), 30s after (PE30s), and at 1, 2, 3, and 4m after 10-s exercise.

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.

PEE-D was found 2m after exercise in LEMS.

PEE-D may be physiologically closest to the reversible myasthenic fatigue after exercise observed in LEMS patients.