A physiological study of the anorectal reflex in patients with functional anorectal and defecation disorders

OBJECTIVE: The symptoms of fecal incontinence and constipation can arise from a variety of alterations of anorectal function. The aim of this study was to investigate components of the anorecal reflex in patients with these symptoms, to determine the functional significance of the various physiological parameters. METHODS: 21 healthy volunteers (controls), 78 incontinent and 74 constipated patients were recruited and symptom burden determined using the Wexner incontinence and constipation questionnaires. All participants underwent standardised anorectal physiology including anorectal manometry, anorectal distension and electrosensitivity thresholds, rectal mucosal blood flow and rectoanal inhibitory reflex measurement. RESULTS: Patients with passive incontinence had lower resting sphincter pressures than controls (38 vs 87cmH2 O, p < 0.05), while those with urge incontinence had lower squeeze pressures than controls (37 vs 119cmH2 O, p < 0.05). Patients with urge incontinence had lower maximal tolerable volumes (100 vs 166mL, p < 0.05). Patients with slow transit constipation had elevated rectal electrosensitivity thresholds compared to controls (31.4 vs 20.2, p < 0.05), and also showed lower mucosal blood flow than patients with evacuation difficult and controls (107 vs 162 (evacuation difficult) vs 169 (controls), p < 0.05). Only patients with passive incontinence were associated with reflex abnormalities (prolonged recovery phase (1.2 vs 0.5 msec, p < 0.05) and total duration of reflex (6.3 vs 4.3 msec, p < 0.05)). CONCLUSION: Anorectal motor, sensory and reflex abnormalities are seen in distinct patterns in patients with fecal incontinence and constipation. This would suggest distinct physiological differences which may predict the potential for different treatment neuromodulation and behavioural modalities in these conditions