Background: Anal sphincter tone is routinely assessed by digital rectal examination in patients with fecal incontinence, although its accuracy in detecting sphincter defects or separating competent from incompetent muscles has not been established.
Objective: In this setting, we aimed to evaluate the accuracy of digital rectal examination in grading anal defects in order to separate small from extensive cases as depicted on 3D endoanal ultrasound, using a scoring sphincter defect and correlate anal tone to anal pressures.
Methods: Women with fecal incontinence were divided into two groups: small or extensive defects according to the ultrasound scoring system. Sensitivity, specificity, positive and negative predictive values of digital rectal examination in grading global and external sphincter defects were calculated. Anal tone at digital rectal examination was compared to resting and incremental pressures.
Results: A cohort of 76 consecutive incontinent women were enrolled. The median Wexner score was 9. Sixty-eight showed sphincter defects on 3D endoanal ultrasound. Anal tone at digital rectal examination was considered abnormal in 62 cases. Abnormal digital rectal examination showed a sensitivity of 90%, specificity of 27.78% in distinguishing small from extensive defects of both sphincters. Five out of eight women with no sphincter defects had only abnormal squeeze tone at digital rectal examination. Abnormal squeeze tone at digital rectal examination had a sensitivity of 65.31% in distinguishing small from extensive external anal sphincter defects. Digital rectal examination sensitivity increased linearly from small to extensive external anal sphincter defects (P=0.001). Women with abnormal resting tone had lower resting pressures than women with normal tone at digital rectal examination (P=0.0001). Women with abnormal squeeze tone had lower incremental pressures than women with normal tone at digital rectal examination (P=0.017).
Conclusion: Digital rectal examination had good sensitivity and poor specificity in discerning small from severe global anal sphincter defects. Moreover, digital rectal examination had fair sensitivity and poor specificity in grading external anal sphincter defects, and its best accuracy was on complete external anal sphincter lesions. Anal resting and squeeze tone were correlated to anal pressures.