The Puborectal Muscle and External Anal Sphincter Can Act Independently of each other in Functional Defecation Disorders

Background: Classification currently used for functional defecation disorders (FDDs) assumes that the puborectal muscle and external anal sphincter act as a single functional unit. We hypothesize that the puborectal muscle and external anal sphincter do not act as a single functional unit. Methods: We performed anorectal manometry and defecometry tests in 124 adult patients suffering from functional defecation disorder. Anorectal manometry provides information about the pressure profile of the anal canal and the distal part of the rectum. The defecometry test provides information about rectoanal coordination during defecation. Results: We observed that the puborectal muscle and external anal sphincter did not always contribute equally to an FDD. We distinguished three main groups of FDDs: congruent (n=105), anal sphincter-dominated (n=10), and puborectal muscle-dominated (n=9). The propulsive force required to defecate (rectal pressure increase) correlated more strongly with pressure increase at the level of the puborectal muscle (ρ=0.794) than at the level of the external anal sphincter (ρ=0.488). Conclusion: We conclude therefore that the puborectal muscle and external anal sphincter do not, by definition, act as a single functional unit in patients suffering from FDDs and may differ in the degree of dyssynergia. Our modified classification of FDDs can significantly improve the proper diagnosis and, therefore, treatment of FDDs. Furthermore, we conclude that isolated high puborectal pressure impedes defecation more than isolated anal sphincter contraction.