Repetitive Nerve Stimulation and Single Fiber EIectromyography Tests for Myasthenia Gravis

Abstract

Sometimes it is not easy to make a diagnosis of myasthenia gravis (MG) when the ocular symptoms are the only clinical manifestations. The authors performed this study to understand the significance or the indication of repetitive nerve stimulation (RNS) and single fiber electromyography (SFEMG) tests in various stages of MG. The subjects consisted of 15 ocular, 12 generalized, 4 remitted MG, and 5 other neurologic diseases which mimicked it.Positive RNS and SFEMG results were found in 53.3%, 86.7% of ocular type, in 0.0%, 75.0% of remitted type, in 75.0%, 91.7% of generalized type of MG and in 0.0%, 60.0% of other neurologic disease, respectively. When we analysed the results in 15 ocular MG and in 5 non-MG groups, the RNS tests had low sensitivity (53.3%) and high specificity (100%) as they were positive in 8 of 15 ocular MG, and negative in all of 5 non-MG group. Whereas the SFEMG had high sensitivity (86. 7%) and low specificity (40.0%) as it was positive in 13 of 15 ocular MG, and negative in 2 of 5 non-MG group.Therefore it would be concluded that the SFEMG test was much more sensitive than the RNS for the diagnosis of MG, but would not differentiate ocular MG from other neurologic diseases whose clinical features mimicked it. On the other hand, the diagnosis of MG would be promising by a positive RNS test as its specificity was very high.