Pelvic muscle electromyography of levator ani and external anal sphincter in nulliparous women and women with pelvic floor dysfunction

OBJECTIVE: The purpose of this study was to compare results of electromyogr aphic assessment of muscular recruitment between nulliparous control subjec ts without pelvic floor dysfunction and parous subjects with genuine stress urinary incontinence and with pelvic organ prolapse. interference pattern analysis is an electromyographic technique that reproducibly measures muscu lar recruitment by detecting both "turns" in the electromyographic signal p roduced by positive and negative peaks of the motor unit potentials and mot or unit potential, amplitude. Fewer turns can indicate loss of motor units or failure of central activation of contraction, whereas greater amplitude can indicate reinnervation after nerve damage. STUDY DESIGN: We performed concentric needle electrode electromyographic ex aminations of the levator ani and external anal sphincter in 15 nulliparous control subjects and 20 parous subjects with abnormalities (n = 9 with gen uine stress urinary incontinence, n = 11 with stage III or IV pelvic organ prolapse). We made digital recordings at multiple sites at rest and with mo derate and maximal contraction. Interference pattern analysis-yielded the n umber of turns per second and the mean signal amplitude tin microvolts) for each site at each contraction level. We compared individual patient data w ith data from the healthy population by means of cloud analysis. Mean value s of number of turns per second and mean amplitude in each group were then compared with nonparametric methods and regression models. RESULTS: Mean ages were 28.7 years (range, 20-49 years) for the control gro up, 54.3 years (range, 35-75 years) for subjects with genuine stress urinar y incontinence, and 65 years (range, 41-77 years) for subjects with pelvic organ prolapse. Median clinical levator ani strengths were 9 (range, 5-9) i n the control group, 5 (range, 2-7) in the genuine stress urinary incontine nce group, and 5 (range, 2-8) in the pelvic organ prolapse group. Median ex ternal anal sphincter strengths were 9 (range, 7-9) in the control group, 5 (range, 3-9) in the genuine stress urinary incontinence group, and 8 (rang e, 4-9) in the pelvic organ prolapse group. The external anal sphincters of subjects with pelvic organ prolapse had the highest percentage of abnormal study results according to cloud analysis. Mean number of turns per second in levators was greater in control subjects than in subjects with abnormal ities (P = .034). We found similar differences in number of turns per secon d for the external anal sphincter (P = .004). In contrast, we did not find differences between groups in mean amplitude in either the levator ani or t he external anal sphincter. Comparison of patients with genuine stress urin ary incontinence versus subjects with pelvic organ prolapse showed no signi ficant difference in the number of turns per second in either muscle. Mean amplitude was greater in the pelvic organ prolapse group than in the genuin e stress urinary incontinence group for both muscles (levator ani, P = .028 ; external anal sphincter, P = .048). Neither mean amplitude nor the number of turns per second could be predicted by clinically estimated levator ani strength, age, or fecal incontinence. CONCLUSION: Compared with nulliparous control subjects, patients with genui ne stress urinary incontinence:and pelvic organ prolapse had changes in the levator ani and external anal sphincter consistent with either motor unit loss or failure of central activation, or both. Subjects with pelvic organ prolapse had findings consistent with greater recovery than was found in th ose with genuine stress urinary incontinence. Measures of recruitment by in terference pattern analysis correlated better with clinical external anal s phincter strength than with levator ani strength and were independent of ag e.