EVALUATION OF REPETITIVE NERVE STIMULATION WITH DIFFERENT STIMULATION FREQUENCIES IN PATIENTS WITH MYASTHENIA GRAVIS

Abstract

Objective: To investigate the effect of voluntary contraction at low frequency repetitive nerve stimulation (RNS) as a sign of presynaptic compensation in patients with Myasthenia Gravis (MG). Material and Method: Thirty-five patients with MG were included. RNS at 3 Hz, recorded from the abductor digiti minimi, trapezius, nasalis, and orbicularis oculi muscles were performed. In muscles with more than 10% decrement, RNS at 1 Hz with 20-90 stimuli was applied after 10-second maximal isometric voluntary muscle contraction (MIVMC). Progressive decremental pattern was considered when decrement values were increasing until the last response. Facilitation after MIVMC was determined by dividing the amplitude of motor response in resting state by the amplitude of the motor response recorded just after contraction. Results: Among 15 patients having RNS at 1 Hz, nine had facilitation after MIVMC. In the muscle with facilitation, there was a significant positive correlation between the increment ratio and the progressive decrement difference between responses 1-4 and 1-9 (correlation coefficient 0.730, p=0.026). Although not statistically significant, muscles showing facilitation following decrement tended to have a progressive decremental pattern. Conclusion: During RNS, facilitation after MIVMC followed by progressive decremental pattern may be related to presynaptic compensation of neuromuscular transmission failure in MG.