Clinical Significance of Axonal Stimulation Single Fiber Electromyography in Patients with Myasthenia Gravis

ABSTRACT

BACKGROUND: The axonal stimulation single fiber electromyography (S-SFEMG) is a relatively new electrophysio-logical technique and has several advantages over conventional voluntarily activated single fiber electromyography (V-SFEMG). This study was performed in patients with myasthenia gravis (MG) in order to analyze their neuromuscular transmission defects and thus to verify the usefulness of the S-SFEMG technique. METHODS: In 44 patients with MG, S-SFEMG was performed on the extensor digitorum communis muscle. The repetitive nerve stimulation test (RNST) on orbicularis oculi, trapezius, flexor carpi ulnaris, and abductor digiti quinti muscles was also performed at the same time. The results of the RNS and S-SFEMG were then analysed in detail. RESULTS: The S-SFEMG was found abnormal in 84.1%, while RNST was found abnormal in 75.0% of the patients tested. The normal S-SFEMG result was observed exclusively among 7 ocular type MG patients. The mean of the mean consecutive difference (MCD) value, % of fibers with blocking and % of fibers with abnormal jitter, was more increased in patients with generalized type MG than those with ocular type MG. This difference was statistically significant (P<0.01) in all 3 variables. CONCLUSIONS The S-SFEMG is a highly sensitive and useful diagnostic tool in MG. Although it demands more strict technical consideration than V-SFEMG, it is less time-consuming and applicable to uncooperative patients including children. Our study shows S-SFEMG to be especially useful in patients with ocular type MG whose RNST results do not show definite decremen-tal responses.