Standardization of anal sphincter electromyography: normative data.
OBJECTIVE
Electromyography (EMG) of the external anal sphincter (EAS) is important in the evaluation of conus/cauda lesions, the differential diagnosis of parkinsonism and anal incontinence. The aim of our study was to establish normative data in a sufficiently large group of healthy subjects, using a rigorously standardized examination technique.


METHODS
Sixty-four subjects (aged 19-83 years) without pelvic or neurological disorders were included. Motor unit potentials (MUPs)/interference pattern (IP) samples were obtained from the EAS using multi-MUP and turn/amplitude analyses, respectively. The effect of age, gender, parity, and constipation on MUP/IP parameters was studied. For MUP parameters the lower/upper limits for mean values, and 'outlier' limits, and for IP parameters normal 'clouds' were calculated.


RESULTS
From 112 muscles 15-30 MUPs were sampled. As no effect of evaluated factors on mean values could be demonstrated, common reference values were calculated. Lower/higher limits for mean values were: amplitude 148/661 microV, duration 3.2/7.8 ms, area 87/625 microVms, and number of phases 2. 3/3.7. 'Outlier' limits for individual MUPs were: amplitude 84/1315 microV, duration 1.6/13.8 ms, area 46/1222 microVms, number of phases 2/6. From 95 muscles 2706 IP samples were obtained.


CONCLUSIONS
The presented normative data should allow valid quantitative EMG of the EAS muscle in patients.
Podnar
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Institute of Clinical Neurophysiology, Division of Neurology, University Medical Centre Ljubljana, SI-1525, Ljubljana, Slovenia. simon.pdnar@kclj.si
Vodusek
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DB
Stâlberg
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E
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000502:physiology*; D004576:Electromyography / Q000592:standards*; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values