Dyssynergic defecation

High resolution anorectal manometry

Anorectal manometry (ARM) is the preferred method for the evaluation of defecatory disorders.^17,18 ARM is best performed using the high-resolution anorectal manometry (HRAM) systems¹⁹ that consist of a flexible probe – 0.5-cm diameter with multiple circumferential sensors along the anal canal – and another two sensors inside a rectal balloon.¹⁸ It provides a topographic and waveform display of manometric pressure data (Figure). The 3D high-definition ARM probe is a rigid 1-cm probe that provides 3D topographic profiles.¹⁸ ARM is typically performed in both the left lateral position and in a more physiological seated position.^20,21 There is considerable variation amongst different institutions on how to perform HRAM, and a recent International Anorectal Physiology Working Group (IAPWG) has provided consensus recommendations for performing this test.²² The procedure for performing HRAM is reviewed elsewhere, but the key elements are summarized below.¹⁸

Push maneuver: On HRAM, after the assessment of resting and squeeze anal sphincter pressures, the patient is asked to push or bear down as if to defecate while lying in left lateral decubitus position. The best of two attempts that closely mimics a normal bearing down maneuver is used for categorizing patient’s defecatory pattern.¹⁸ In patients with DD, at least four distinct dyssynergia phenotypes have been recognized (Figure),²³ though recent studies suggest eight patterns.²⁴ Defecation index (maximum rectal pressure/minimum residual anal pressure when bearing down) greater than 1.2 is considered normal.¹⁸

Simulated defecation on commode: The subject is asked to attempt defecation while seated on a commode with intrarectal balloon filled with 60 cc of air, and both the defecation pattern(s) and defecation index are calculated. A lack of coordinated push effort is highly suggestive of DD.²¹

Rectoanal Inhibitory Reflex (RAIR): RAIR describes the reflex relaxation of the internal anal sphincter after rectal distension. RAIR is dependent on intact autonomic ganglia and myenteric plexus²⁵and is mediated by the release of nitric oxide and vasoactive intestinal peptide.²⁶ The absence of RAIR suggests Hirschsprung disease.^22.27.28

Rectal sensory testing: Intermittent balloon distension of the rectum with incremental volumes of air induces a range of rectal sensations that include first sensation, desire to defecate, urgency to defecate, and maximum tolerable volume. Rectal hyposensitivity is diagnosed when two or more sensory thresholds are higher than those seen in normal subjects^29.30 and likely results from disruption of afferent gut-brain pathways, cortical perception/rectal wall dysfunction, or both.²⁹ Rectal hyposensitivity affects 40% of patients with constipation³⁰and is associated with DD but not delayed colonic transit.³¹ Rectal hyposensitivity may also be seen in patients with diabetes or fecal incontinence.¹⁸ About two-thirds of patients with rectal hyposensitivity have rectal hypercompliance, and some have megarectum.³² Some patients with DD have coexisting irritable bowel syndrome (IBS) and may have rectal hypersensitivity.^18,33 Rectal compliance is measured alongside rectal sensitivity analysis by plotting a graph between the change in intraballoon volume (mL) and change in intrarectal pressures (mm Hg) during incremental balloon distensions.^18.34 Rectal hypercompliance may be seen in megarectum and dyssynergic defecation.^34,35 Rectal hypocompliance may be seen in patients with inflammatory bowel disease, postpelvic radiation, chronic ischemia, and advanced age.¹⁸

Balloon expulsion test: This test is performed by placing a plastic probe with a balloon in the rectum and filling it with 50 cc of warm water. Patients are given 5 minutes to expel the balloon while sitting on a commode. Balloon expulsion time of more than 1 minute suggests a diagnosis of DD,²¹ although 2 minutes provides a higher level of agreement with manometric findings.³⁶ Balloon type and body position can influence the results.³⁷ Inability to expel the balloon with normal manometric findings is considered an inconclusive finding per the recent London Classification (i.e., it may be associated with generation of anorectal symptoms, but the clinical relevance of this finding is unclear as it may also be seen in healthy subjects).²²