Standardization of anal sphincter electromyography: normative data

Objectives: Electromyography (EMG) of the external anal sphincter (EAS) is important in the evaluation of conus/cauda lesions, the differential diagno sis of parkinsonism and anal incontinence. The aim of our study was to esta blish normative data in a sufficiently large group of healthy subjects, usi ng a rigorously standardized examination technique. Methods: Sixty-four subjects (aged 19-83 years) without pelvic or neurologi cal disorders were included. Motor unit potentials (MUPs)/interference patt ern (IP) samples were obtained from the EAS using multi-MUP and turn/amplit ude analyses, respectively. The effect of age, gender, parity, and constipa tion on MUP/IP parameters was studied. For MUP parameters the lower/upper l imits for mean values, and 'outlier' limits, and for TP parameters normal ' clouds' were calculated. Results: From 112 muscles 15-30 MUPs were sampled. As no effect of evaluate d factors on mean values could be demonstrated, common reference values wer e calculated. Lower/higher limits for mean values were: amplitude 148/661 m uV, duration 3.2/7.8 ms, area 87/625 mu Vms, and number of phases 2.3/3.7. 'Outlier' limits for individual MUPs were: amplitude 84/1315 muV, duration 1.6/13.8 ms, area 46/1222 mu Vms, number of phases 2/6. From 95 muscles 270 6 IP samples were obtained. Conclusions: The presented normative data should allow valid quantitative E MG of the EAS muscle in patients. (C) 2000 Elsevier Science ireland Ltd. Al l rights reserved.