Comparison of different outlier criteria in quantitative anal sphincter electromyography.
OBJECTIVE
Analysis based on 'outliers' has been demonstrated to be a useful adjunct to mean value analysis in quantitative needle electromyography (EMG). However, the outlier criteria applied have been arbitrarily chosen. The aim of the present study was to determine the most useful outlier criteria in motor unit potential (MUP) analysis.


METHODS
The external anal sphincter (EAS) muscles were examined by multi-MUP analysis. From 115 muscles of 64 normative subjects, the 0/100, 5/95, 10/90, 15/85, 20/80, and 25/75 percentile MUP parameter values were grouped individually. From these, the 5/95, 2.5/97.5, 1/99 and 0/100% confidence limits were determined. Thus, 24 sets of outlier limits were formed. To calculate sensitivity and specificity, data from 79 patients with cauda equina lesions (189 muscles), and from 77 controls (119 muscles) were compared to normative outlier limits.


RESULTS
Sensitivities were highest with outlier limits formed from the 10-90 percentile ranges, followed by the 5-95 and 15-85 percentile ranges, while specificity was highest using the 15-85, followed by the 20-80, and 25-75 percentile ranges. On direct head-to-head comparison the 10-90 percentile ranges were more sensitive and 5-95 were more specific.


CONCLUSIONS
The study demonstrated considerable differences in the sensitivity and specificity of outlier limits calculated from different percentile ranges, with outlier criteria calculated from the 10-90 and from the 5-95 percentile ranges appearing to be the most useful for detection of neuropathy in the EAS muscle.


CONCLUSIONS
In future EAS muscle EMG I propose that outlier criteria calculated from the 10-90 percentile ranges be used.
Division of Neurology, Institute of Clinical Neurophysiology, University Medical Center Ljubljana, Zaloska cesta 7, SI-1525 Ljubljana, Slovenia. simon.podnar@kclj.si
Simon
S
Podnar
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000502:physiology*; D016022:Case-Control Studies; D002420:Cauda Equina; D002648:Child; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D010523:Peripheral Nervous System Diseases / Q000150:complications; D012016:Reference Values; D012680:Sensitivity and Specificity; D013223:Statistics as Topic