Normal values of single fiber EMG on extensor digitorm communis muscle with volundery activaction using "off line" analysis method

29 VII. SUMMARY Single fiber EMG analysis is usually performed with "on-line" method during recording. However, this technique usually prolongs the study and makes re- analysis impossible. Published normal values can not be used with analogous tape recordings due to the additional latency brought about by the elasticity of the tape. We compared jitter values obtained from normal volunteers without neuromuscular transmission disorders with "on-line" measurement peviously puplished. We performed single fiber EMG with voluntary activation on extensor digitorum communis muscle of 25 first-degree relatives of juvenile myasthenia gravis patients. All potentials were recorded on tape. Fiber density was estimated from 20 different recording sites. 5 to 18 potential pairs were studied in each subject. Mean(SD) (95th percentile) fiber density was 1.60(0.18)(1.90). Mean highest jitter was 31.24(6.87)(47.00). Mean jitter was 25.08(5.04)(43.00) microseconds. Mean interpotential interval was 0.67(0.1 1)(0.91) miliseconds. Although upper normal limit for individual pairs did not significantly differ from values obtained by "on-line" analysis, upper normal limit for mean jitter was increased about 5 miliseconds. We believe that this variation results from the tape recorder technique. These values can be used in the investigation of native population. Due to the fact that relatively young age of the group we studied, previously puplished values should be utilized in the evaluation of subjects over 60 years of age.