Reference values for voluntary and stimulated single-fibre EMG using concentric needle electrodes: A multicentre prospective study

ObjectiveThe aim of this study is to establish reference values for single-fibre electromyography (SFEMG) using concentric needles in a prospective, multicentre study.MethodsVoluntary or stimulated SFEMG at the extensor digitorum communis (EDC) or frontalis (FRO) muscles was conducted in 56–63 of a total of 69 normal subjects below the age of 60 years at six Japanese 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.ResultsThe cut-off values for individual MCD (+2.5 SD) were 56.8 μs for EDC-V (voluntary SFEMG for EDC), 58.8 μs for EDC-S (stimulated SFEMG for EDC), 56.8 μs for FRO-V (voluntary SFEMG for FRO) and 51.0 μs for FRO-S (stimulated SFEMG for FRO). The false positive rates using these cut-off values were around 2%.ConclusionsThe +2.5 SD and 95% prediction limit might be two optimal cut-off values, depending on the clinical question. The obtained reference values were larger than those reported previously using concentric needles, but might better coincide with conventional values.SignificanceThis is the first multicentre study reporting reference values for SFEMG using concentric needles. The way to determine cut-off values and the statistically correct definition of the percentile were discussed.

► The reference values for both voluntary and stimulated concentric SFEMG in the EDC and frontal muscles were constructed.
► The reference values obtained in this study were larger than those reported previously for concentric needles.
► Appropriate definitions of the percentile and cut-off values were discussed.