A comparative study of single fiber electromyography and repetitive nerve stimulation of the same extensor digitorum communis muscle in patients with myasthenia gravis / 中华物理医学与康复杂志

ABSTRACT

Objective To investigate the possible causes of the different diagnostic sensitivity of voluntary single fiber electromyography (SFEMG) and repetitive nerve stimulation(RNS) in patients with myasthenia gravis (MG). Methods The voluntary SFEMG and RNS at low rates were recorded successively from the same extensor digitorum communis (EDC) muscle on the same day in 67 patients with MG. Results The diagnostic sensitivity of SFEMG and RNS was 92.5% and 50.7%, respectively, with the former statistically significantly higher than the later. The percentage of decrement of RNS was positively correlated with 3 SFEMG parameters, i.e. the mean jitter, percentage of abnormal pairs of potential and percentage of impulse blocking. Among the 34 cases with significant decrement on RNS, 2 had no impulse blocking and the maximum decrement reached 62%, while 33 cases with normal RNS had up to 58% of impulse blocking. Conclusion The voluntary SFEMG was more sensitive than RNS in diagnosing MG even in the same muscle. The blocking phenomenon observed in voluntary SFEMG was not completely corresponding to the decrement in RNS.The possible explanations were partly because that RNS recorded the total muscle fibers response in surface of the muscle and SFEMG examined the increasing or blocking at individual motor end-plates, and partly because that the voluntary SFEMG and RNS might explored endplates belonging to different motor units.