[Reference values for concentric needle single fiber EMG].

Single-fiber electromyography (SFEMG) is one of the most sensitive diagnostic tests of myasthenia gravis. Single-fiber needle electrodes were used originally, however, disposable concentric needle electrodes have been used increasingly in recent years to avoid infection. We therefore undertook a prospective, multicenter study to establish reference values of concentric needle SFEMG in Japanese subjects for both voluntary and stimulated SFEMG and for two commonly examined muscles, the extensor digitorum communis (EDC) and the frontalis (FRO). 69 normal subjects below the age of 60 years were enrolled at six institutes. The cut-off values for mean consecutive difference (MCD) of individual potentials were calculated using+2.5 SD or 95% prediction limit (one-tail) of the upper 10th percentile MCD value for individual subjects. The recommended cut-off values for individual MCD were 56.8 μs for voluntary SFEMG for EDC, 58.8 μs for stimulated SFEMG for EDC, 56.8 μs for voluntary SFEMG for FRO and 51.0 μs for stimulated SFEMG for FRO. This is the first multicenter study reporting reference values for SFEMG using concentric needles.