A study on post-exercise facilitation in 11 patients with Lambert-Eaton myasthenic syndrome

Abstract

Objective To study the operation method of the post-exercise facilitation (PEF) in Lambert-Eaton myasthenic syndrome (LEMS), and to seek for the meaning of PEF in clinical work. Methods Eleven patients with LEMS were included to accept the PEF and the repetitive nerve stimulation (RNS) test. When performing the PEF test, compound muscle action potentials (CMAPs) of abductor digitiminimi were recorded after a specified time of exercise. The patients would get rest for 1 minute before the next test. The same exercises were repeated for several times. The exercise time started from 0 second, and 2 seconds was added each time until the CMAP did not increase. The PEF or RNS test was followed by a continuous stimuli at 0.5 Hz and the CMAPs were recorded to study the recovery process. Results The CMAPs of abductor digitiminimi increased significantly after PEF. The median time for CMAPs to achieve its maximum was 12(10, 14) seconds. The recovery processes of PEF and RNS showed that the CMAP would return to normal after (50.4±16.0) seconds. Conclusions Patients with suspected LEMS might get a 10-12 seconds of PEF test instead of RNS for it is fast and painless. If the potential of CMAPs increased ≥60%, the result would be positive. If the potential of CMAPs increased ≤24%, the result would be negative. A suspicious increments of CMAPs (increasing by 24%-60%) should warrant a further RNS test. And the interval between the two tests should be longer than (50.4±16.0) seconds. Key words: Lambert-Eaton myasthenic syndrome; Post-exercise facilitation; Electric stimulation; Electrophysiology