Correlations between electrophysiological parameters of repetitive nerve stimulation and single fiber electromyography tests in myasthenia gravis

J Korean Neurol Assoc > Volume 16(3); 1998 > Article

Journal of the Korean Neurological Association 1998;16(3): 366-371.

중증근무력증 환자에서 반복신경자극검사와 단섬유근전도검사의 전기생리학적 지표들의 상관관계에 대한 연구

김종민, 최성혜 이광우

서울대학교 의과대학 신경과학교실

Correlations between electrophysiological parameters of repetitive nerve stimulation and single fiber electromyography tests in myasthenia gravis

Jong-Min Kim, M.D., Sung-Hye Choi, M.D., Kwang-Woo Lee, M.D.

Department of Neurology, Seoul National University College of Medicine

Abstract

Background and Purpose : For diagnosis of acquired autoimmune myasthenia gravis (MG), single fiber electromyography (SFEMG) is known to be much more sensitive than repetitive nerve stimulation test (RNST) in demonstrating the electrophysiological defects of neuromuscular transmission. Neuromuscular blocking in SFEMG is presumed to have the same physiologic basis with decremental response in RNST. The authors performed the study to know the correlations between the electrophysiological parameters of the RNST (decremental response) and the SFEMG (jitter and blocking) and to understand the basic physiological mechanisms in MG. Methods : In 28 patients with definite MG (12 : ocular MG, 16 : generalized MG), RNST and SFEMG tests were done in orbicularis oculi and abductor digiti quinti and in extensor digitorum communis, respectively. The correlations between several factors, such as maximum decremental response (%) in RNST, mean value of mean consecutive differences (MCD’s) (?sec) and blocking pairs (%) were analyzed. Results : In 12 ocular MG patients, RNST and SFEMG abnormalities were found in 4 (33.3%) and in 10 (83.3%), respectively. In 16 generalized MG patients, abnormal decremental responses were found in 13 (81.3%) and increased jitters in 15 (93.8%). SFEMG showed significant correlations between blockings and mean MCD’s (R=0.54, p<0.01). When the correlation between RNST and SFEMG was analyzed, increased percentage of blockings in extensor digitorum communis were correlated with maximum degree of decremental responses in abductor digiti quinti or orbicularis oculi (R=0.60, p<0.001). The degree of mean MCD’s was poorly correlated with maximum decremental responses (R=0.23, p=0.229). But the correlation became significant (R=0.43, p<0.05) by analyzing mean MCD’s and maximum decremental responses only from abductor digiti quinti, reflecting that blockings have similar electrophysiological meanings with increased mean MCD’s, Conclusion : The good correlation between decremental response in RNST and blocking or mean MCD’s in SFEMG was found. Therefore the authors concluded that the parameters of the RNST and the SFEMG show similar electrophysiologic phenomena of the abnormal neuromuscular transmission in MG. Key Words : single fiber electromyography, repetitive nerve stimulation test, myasthenia gravis