Does Water-Perfused Catheter Overdiagnose Anismus Compared to Balloon Probe?

Background: The purpose of this study was to compare the manometric assessment of straining effort as if to defecate and rectoanal inhibitory reflex obtained with a rectosphincteric balloon probe and with a waterperfused catheter in the same subject. Methods: Twelve healthy volunteers underwent two manometric assessments of anal sphincter function and electromyographic (EMG) surface recordings, one with a rectosphincteric balloon and one with a water-perfused catheter, 7 days apart in random order. Results: Increased EMG activity in the external anal sphincter in the midst of the rectoanal inhibitory reflex ( P < 0.001) and during straining for defecation ( P < 0.001) was more frequently observed with the perfused system than with the balloon probe. There was a discrepancy between the EMG activity of the external anal sphincter and the anal pressures during straining recorded with the perfused system. Duration of the reflex elicited by rectal distension with 10 and 20 ml of air was significantly greater with the rectosphincteric balloon than with the perfused catheter ( P = 0.02 and P = 0.05, respectively). Conclusion: Water instilled in the anal canal by the perfused system induces artifacts in EMG recording and active anal contractions. These artifacts and induced contractions could lead to an erroneous diagnosis of anismus, particularly if pelvic floor EMG is only taken into account for the diagnosis of anismus.