Concentric needle single fiber electromyography: normative jitter values on voluntary activated Extensor Digitorum Communis.

Single fiber electromyography (SFEMG) is the most sensitive clinical neurophysiological test for neuromuscular junction disorders, particularly myasthenia gravis. Normal values for jitter obtained with SFEMG electrode have been published, but there are few publications for concentric needle electrode (CNE). The aim of this study was to discuss the possibilities to analyse the jitter in CNE recordings and to get normal values of jitter for voluntary activated Extensor Digitorum Communis using disposable CNE. Fifty normal subjects were studied, 16 male and 34 female with a mean age of 37.1+/-10.3 years (19-55). The jitter values of action potentials pairs of isolated muscular fibers were expressed as the mean consecutive difference (MCD) after 20 analysed potential pairs. The mean MCD (n=50) obtained was 24.2+/-2.8 micros (range of mean values in each subject was 18-31). Upper 95% confidence limit is 29.8 micros. The mean jitter of all potential pairs (n=1000) obtained was 24.07+/-7.30 micros (range 9-57). A practical upper limit for individual data is set to 46 micros. The mean interpotential interval (MIPI) was 779+/-177 micros (range of individual mean values was 530-1412); there were no potentials with impulse blocking. The present study confirms that CNE is suitable for jitter analysis although certain precautions must be mentioned. Our findings of jitter values with CNE were similar to some other few reports in literature.