Pitfalls and limitations of testing the rectoanal inhibitory reflex in screening for Hirschsprung's disease

Problems in testing the absence or presence of the rectoanal inhibitory reflex (RAIR) were analyzed in 261 consecutive patients referred to confirm or exclude Hirschsprung's disease. Confident interpretation of the manometric record was possible in 89% of the cases. False results were observed in 9 patients (4%): false-negative tests (the presence of Hirschsprung's disease could not be identified) in 2 and false-positive tests (inability to induce a RAIR in patients who turned out not to have Hirschsprung's disease) in 7. In 11% the manometric result was equivocal. The value of anorectal manometry was most limited below the age of 1 month.Equivocal and false manometric results can be limited by: (1) avoiding anal stretching just before manometry; (2) avoiding restlessness during the examination; (3) leaving the catheter of the rectal distending balloon unfixed; (4) exact positioning of the pressure-recording devices in the anal canal; (5) regular checks of the position of the distending and recording devices; (6) distending the rectal ampulla until the rectal sensation level is reached; and (7) strict application of the characteristic features of a normal RAIR during analysis, i.e. a reproducible and progressive anal pressure decrease followed by recovery of the basal tone or transient inhibition of anal pressure waves induced by rectal distension. While a rectal biopsy remains the golden standard for final diagnosis, anorectal manometry is preferable for screening but should be complemented by biopsy if the first examination is equivocal, if the RAIR is absent, or when the clinical condition an/or the result of contrast enema conflict with a negative manometric test. A high degree of manometric accuracy can be reached after adequate initiation, as evidenced by the comparable performances of the five examiners in this study with different degrees of expertise.Offprint requests to: F. Penninckx