Anorectal physiology in relation to clinical subgroups of patients with severe constipation

Abstract

The aim of this study was to evaluate anorectal physiology in relation to clinically defined subgroups of patients with idiopathic constipation and to analyse relationships between anorectal physiology and rectal evacuation. One hundred consecutive patients with idiopathic constipation were clinically categorized as slow transit (n=19), outlet obstruction (n=52) and a group with mixed symptoms (n=29). They were examined by recording anal pressures and also rectal volumes in response to stepwise increases in rectal pressure (5-60 cm H2O). The manovolumetric results were compared with 28 sex and aged matched controls. Rectal evacuation was measured by computer-based image analysis of rectal emptying rate in defaecography. The rectal pressure thresholds for filling, urge and pain did not differ between the groups but there were proportionally more patients in the slow transit and mixed group with thresholds for filling exceeding 25 cm H2O (P=0.04). In total, 18% of patients had impaired sensitivity which was associated with long duration of symptoms (P < 0.05). Patients with grossly impaired rectal sensitivity (filling threshold > 40 cm H2O) had impaired rectal evacuation (P < 0.05). The rectal compliance was increased in the slow transit and mixed group (P < 0.01-0.05) in the pressure interval 5-15 cm H2O. Anal resting and squeeze pressures did not differ between the groups although 7/19 in the slow transit group had values around the lower limit of controls. Slow wave frequency was lower in all patient groups (P < 0.001 vs. controls). Rectal evacuation was not related to sphincter function or to rectal compliance. Clinical categorization of constipated patients defines groups where altered anorectal physiology is not uncommon. Constipation with symptoms of infrequent defaecation may be associated with impaired rectal sensitivity and increased rectal compliance whereas outlet obstruction symptoms are not clearly related to changes in anorectal physiology.