Methods of anorectal physiology

Abstract

Anorectal physiology involves the complex coordination of pelvic muscles and nerves which facilitates appropriate bowel function. There are various anatomical and functional tests available to evaluate anorectal physiology and thereby differentiate underlying causes of a range of anorectal disorders, including fecal incontinence, constipation, and rectal pain. These methods include anorectal manometry (ARM), balloon expulsion test (BET), electromyography, and pudendal nerve latency testing. This article will discuss the components of these tests, how they measure various aspects of anorectal function, and how those results then guide treatment for each disorder. This article will also review the London Classification for Disorders of Anorectal Function, which was established in 2020 by the International Anorectal Physiology Working Group (IAPWG) and has become the gold standard for measuring disorders of anorectal function. The London Classification has standardized the testing protocols and results interpretation of ARM and balloon expulsion testing to assist in the differentiation of specific types of bowel dysfunction. This protocol classifies disorders under four distinct groups: disorders of the rectoanal inhibitory reflex, disorders of anal tone and contractility, disorders of rectoanal coordination, and disorders of rectal sensation. The London Classification not only standardizes ARM testing protocols but also the language used to describe anorectal function, to better define anorectal disorders and treatment guidelines and thereby improve clinical outcomes.