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2 passages
A) Exercise testing in Lambert-Eaton myasthenic syndrome, with the median nerve stimulated supramaximally at the wrist and the abductor pollicis brevis muscle recorded. Top: Baseline. Bottom: Immediately after 10 seconds of maximal voluntary exercise. Note marked increase in compound muscle action potential amplitude (postexercise facilitation). Preexercise and postexercise testing, looking for an increment, always is better tolerated by patients than is 50-Hz repetitive nerve stimulation.
B) Slow (3 Hz) repetitive nerve stimulation in LEMS, before and after brief exercise. In both situations, there is a prominent decrement. However, after brief exercise, the baseline compound muscle action potential (CMAP) is significantly larger compared with the CMAP before exercise. In this case, the CMAP increment after brief exercise was 2000 percent. CMAP: compound muscle action potential. Reproduced with permission from: Preston, DC, Shapiro, BE. Electromyography and Neuromuscular Disorders, 2nd ed, Butterworth-Heinemann, Boston 1998. Copyright © 1998 Elsevier.