One and Done: Is Measurement of the Rectoanal Pressure Gradient Enough to Diagnose Defecatory Disorders and Guide the Management of Constipation?

Abstract

See “Comparison of anorectal manometry, rectal balloon expulsion test, and defecography for diagnosing defecatory disorders” by Blackett RW, Gautam M, Mishra R, et al, on page 1582. See “Comparison of anorectal manometry, rectal balloon expulsion test, and defecography for diagnosing defecatory disorders” by Blackett RW, Gautam M, Mishra R, et al, on page 1582. Constipation and related issues, such as difficulty evacuating stool (“outlet obstruction”), are common in the community. Many patients with these symptoms are not satisfied with standard treatment, including osmotic and stimulant laxatives.1Muller-Lissner S. Tack J. Feng Y. et al.Levels of satisfaction with current chronic constipation treatment options in Europe—an internet survey.Aliment Pharmacol Ther. 2013; 37: 137-145Crossref PubMed Scopus (81) Google Scholar Initial investigations, including colonoscopy, rarely identify an obstructive tumor or another “organic” disease as a cause of symptoms. In this situation, guidelines recommend referral for investigations of anorectal function, in particular, high-resolution anorectal manometry (HR-ARM), to identify the causes of symptoms and to guide more effective treatment.2Carrington E.V. Scott S.M. Bharucha A. et al.Expert consensus document: advances in the evaluation of anorectal function.Nat Rev Gastroenterol Hepatol. 2018; 15: 309-323Crossref PubMed Scopus (122) Google Scholar,3Wald A. Bharucha A.E. Limketkai B. et al.ACG Clinical Guidelines: management of benign anorectal disorders.Am J Gastroenterol. 2021; 116: 1987-2008Crossref PubMed Scopus (29) Google Scholar Defecatory disorder or “dyssynergic defecation” (DD) is an important cause of outlet obstruction and constipation that often fails to respond to oral medications. Different forms of DD are recognized that involve paradoxical contraction of the anal sphincter or the failure to generate abdominal pressure during defecation, or both.4Carrington E.V. Heinrich H. Knowles C.H. et al.The International Anorectal Physiology Working Group (IAPWG) recommendations: standardized testing protocol and the London Classification for disorders of anorectal function.Neurogastroenterol Motil. 2020; 32e13679Crossref PubMed Scopus (107) Google Scholar Identifying this abnormal behavior is a key aim of HR-ARM, with direct impact on clinical management. Prospective studies report that individuals with DD have a high likelihood of symptom resolution with specialized pelvic floor physiotherapy with biofeedback,5Chiarioni G. Salandini L. Whitehead W.E. Biofeedback benefits only patients with outlet dysfunction, not patients with isolated slow transit constipation.Gastroenterology. 2005; 129: 86-97Abstract Full Text Full Text PDF PubMed Scopus (285) Google Scholar, 6Chiarioni G. Whitehead W.E. Pezza V. et al.Biofeedback is superior to laxatives for normal transit constipation due to pelvic floor dyssynergia.Gastroenterology. 2006; 130: 657-664Abstract Full Text Full Text PDF PubMed Scopus (316) Google Scholar, 7Rao S.S. Seaton K. Miller M. et al.Randomized controlled trial of biofeedback, sham feedback, and standard therapy for dyssynergic defecation.Clin Gastroenterol Hepatol. 2007; 5: 331-338Abstract Full Text Full Text PDF PubMed Scopus (283) Google Scholar a technique that teaches the patient how to restore the effective coordination between abdominal wall contraction and anal canal relaxation required for defecation. DD can be diagnosed by HR-ARM or a test of rectal evacuation such as balloon expulsion test (BET) or conventional or magnetic resonance (MR) defecography. HR-ARM is simple to perform and provides a visually intuitive, continuous assessment of pressure activity in the rectum and anal canal during simulated defecation; however, the interpretation of test results is complicated by disagreements on protocol and data interpretation. Additionally, it has been reported that many healthy controls show increased pressure in the anal canal during simulated defecation that cannot be distinguished from DD using conventional measurements.8Grossi U. Carrington E.V. Bharucha A.E. et al.Diagnostic accuracy study of anorectal manometry for diagnosis of dyssynergic defecation.Gut. 2016; 65: 447-455Crossref PubMed Scopus (127) Google Scholar Similar limitations apply to BET and imaging studies.2Carrington E.V. Scott S.M. Bharucha A. et al.Expert consensus document: advances in the evaluation of anorectal function.Nat Rev Gastroenterol Hepatol. 2018; 15: 309-323Crossref PubMed Scopus (122) Google Scholar For this reason, the perception of many clinicians is that HR-ARM has limited utility, and patients with obstructive defecation are often referred for biofeedback without prior testing. The problem with this approach is that access to specialist pelvic floor physiotherapy is limited, costs are incurred, and patients with slow-transit constipation or structural causes of outlet obstruction (more than half of the total) are unlikely to benefit from this intervention.5Chiarioni G. Salandini L. Whitehead W.E. Biofeedback benefits only patients with outlet dysfunction, not patients with isolated slow transit constipation.Gastroenterology. 2005; 129: 86-97Abstract Full Text Full Text PDF PubMed Scopus (285) Google Scholar,6Chiarioni G. Whitehead W.E. Pezza V. et al.Biofeedback is superior to laxatives for normal transit constipation due to pelvic floor dyssynergia.Gastroenterology. 2006; 130: 657-664Abstract Full Text Full Text PDF PubMed Scopus (316) Google Scholar In response to these concerns, expert opinion, as set out in the London Classification, an international consensus classification for disorders of anorectal function, advocates that 2 complimentary tests be performed to establish the diagnosis of DD—1 of anorectal function (HR-ARM) and 1 of rectal evacuation (BET, defecography).4Carrington E.V. Heinrich H. Knowles C.H. et al.The International Anorectal Physiology Working Group (IAPWG) recommendations: standardized testing protocol and the London Classification for disorders of anorectal function.Neurogastroenterol Motil. 2020; 32e13679Crossref PubMed Scopus (107) Google Scholar A retrospective clinical database study published in this issue of Gastroenterology provides important data that validates this methodology and refines the HR-ARM criteria used to diagnose DD in clinical practice.9Blackett R.L. Gautam M. Mishra R. et al.Comparison of anorectal manometry, rectal balloon expulsion test, and defecography for diagnosing defecatory disorders.Gastroenterology. 2022; 163: 1582-1592Abstract Full Text Full Text PDF Scopus (2) Google Scholar Predominantly female, healthy controls and patients referred for investigations of anorectal function were studied. Defecography provided an independent assessment of rectal evacuation. The performance of HR-ARM measurements, including the rectoanal pressure gradient (RAPG) during simulated defecation, and BET in the diagnosis of DD was analyzed. Among patients with constipation, the probability of impaired rectal evacuation on defecography was only 45% when 1 test result was abnormal, but 75% when the results of both variables were abnormal. Additionally, lower anal squeeze pressure and rectal hyposensitivity were associated with inability to empty the rectum. These findings support the clinical utility of HR-ARM in the assessment of patients with outlet obstruction; however, there are technical and methodological challenges to the use of pressure measurements in the assessment of a complex process such as defecation. Early HR-ARM studies reported a very high frequency of abnormal anal pressure during simulated defecation in healthy controls and patients8Grossi U. Carrington E.V. Bharucha A.E. et al.Diagnostic accuracy study of anorectal manometry for diagnosis of dyssynergic defecation.Gut. 2016; 65: 447-455Crossref PubMed Scopus (127) Google Scholar; however, this was based on conventional line tracings and did not use the full information available from HR-ARM spatiotemporal pressure plots. It is now clear that a complete relaxation of the anal sphincter down to atmospheric pressure, as shown in textbooks, does not reflect normal physiology. During defecation, there is a build-up of abdominal pressure at the same time as anal relaxation. When the abdominal pressure is greater than the anal pressure, the sphincter opens. At this moment, there is equilibration of pressure in the rectum and anal canal, generating sufficient propulsive force to drive evacuation (Figure 1A). RAPG, the measurement validated by Blackett et al,9Blackett R.L. Gautam M. Mishra R. et al.Comparison of anorectal manometry, rectal balloon expulsion test, and defecography for diagnosing defecatory disorders.Gastroenterology. 2022; 163: 1582-1592Abstract Full Text Full Text PDF Scopus (2) Google Scholar captures this information by integrating rectal/abdominal pressure and pressure in the anal canal. Although RAPG provides a far superior assessment of defecation than any point measurement of rectoanal pressure, it remains dependent on investigator and patient factors. For example, it has been shown that investigations in the physiological, upright position improve compliance and that patients who receive enhanced instruction during HR-ARM have significantly higher RAPG with less frequent findings suggestive of DD.10Heinrich H. Fruehauf H. Sauter M. et al.The effect of standard compared to enhanced instruction and verbal feedback on anorectal manometry measurements.Neurogastroenterol Motil. 2013; 25: 230-237.e163Crossref PubMed Scopus (42) Google Scholar Additionally, normal reference limits and a clear pathological threshold for RAPG have not yet been established, and any such threshold will depend on catheter design and patient factors, including sex and parity. Another criticism of RAPG is that it cannot on its own differentiate functional and structural pathology as a cause of outlet obstruction. By contrast, qualitative assessment of spatiotemporal plots during defecation appears to provide a more meaningful assessment of anorectal function than quantitative measurements. A negative RAPG is not always generated by paradoxical contraction of the anal sphincter. Comparison of HR-ARM findings during voluntary squeeze and simulated defecation can make this obvious (Figure 1B). Studies that compare HR-ARM with MR defecography show that this technique can visualize pelvic floor descent with failure of the anal sphincter to open and also that a narrow pressure band in the anal canal during simulated defecation indicates the presence of structural obstruction (Figure 1C).11Heinrich H. Sauter M. Fox M. et al.Assessment of obstructive defecation by high-resolution anorectal manometry compared with magnetic resonance defecography.Clin Gastroenterol Hepatol. 2015; 13: 1310-1317.e1Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar,12Mion F. Garros A. Brochard C. et al.3D high-definition anorectal manometry: values obtained in asymptomatic volunteers, fecal incontinence and chronic constipation. Results of a prospective multicenter study (NOMAD).Neurogastroenterol Motil. 2017; 29e13049Crossref Scopus (47) Google Scholar Efforts continue to identify objective biomarkers from HR-ARM spatiotemporal plots that more fully capture the underlying pathophysiological mechanism of disease. In conclusion, the study confirms that a negative RAPG on HR-ARM and a failed BET can help to establish the cause of outlet obstruction and constipation. The authors propose that both findings are required for a conclusive diagnosis (“definite dyssynergia”), whereas 1 abnormal finding should be considered “probable dyssynergia.” In the latter case, defecography should be considered to confirm the diagnosis or to identify other causes of disease. This validation of current guidelines will likely improve acceptance of physiological investigations of anorectal function by clinicians and surgeons. To assess the clinical utility of HR-ARM in this situation, prospective studies are now needed to confirm that an abnormal RAPG predicts treatment outcome in patients with DD. Comparison of Anorectal Manometry, Rectal Balloon Expulsion Test, and Defecography for Diagnosing Defecatory DisordersGastroenterologyVol. 163Issue 6PreviewA reduced rectoanal gradient, compared with age- and sex-matched asymptomatic individuals, was the most important parameter on anorectal manometry to predict impaired evacuation by balloon expulsion test or defecography and should be considered probable evidence of a defecatory disorder. Full-Text PDF