Sphincter electromyography (EMG) is an important method in diagnosis of neuropathic sacral lesions. Quantitative EMG analysis increases utility of the test, but requires valid reference values. Although commonly employed, validity of sharing reference data between electrodiagnostic laboratories has not been confirmed. In this study, this approach was assessed by comparing the reproducibility of data sets obtained by the same and different laboratories.
Confidence intervals and sensitivity of motor unit potential (MUP) parameters in the external anal sphincter (EAS) muscles were calculated using data obtained from 3 different control groups of women (number of women: 41, 48 and 66), examined by the same (the first two groups) and another investigator (the third group). Sensitivities to diagnose neuropathic changes in a known patient group were compared.
When compared to the first reference group, the MUP parameter means of 2/7 (same investigator) vs. 3/7 (different investigator) were significantly different. Similarly, 3/14 vs. 4/14 MUP parameter outliers were different. Finally, 6/14 vs. 7/14 sensitivities (using a combination of MUP parameter means and outliers) were different.
This study demonstrated somewhat larger differences between confidence intervals obtained by different investigators, as compared to those obtained by a single investigator. However, most of these differences can be explained by differences in recruited groups of women, and slight inconsistencies in applied techniques. Presented data suggest that confidence intervals from other laboratories can be used, but only if exact protocols from original normative studies are strictly followed.