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

Fecal incontinence (FI) and constipation can arise from a variety of alterations of anorectal function. This study aimed to investigate the components of the anorecal reflex in patients with these symptoms and to determine the functional significance of various physiological parameters.

Altogether 21 healthy volunteers (controls) and 78 FI-predominant and 74 constipation-predominant patients were recruited and administered Wexner incontinence and constipation questionnaires. All participants underwent standardized anorectal physiology assessments.

Patients with passive FI had lower resting sphincter pressures than controls (38 cmH₂ O vs 87 cmH₂ O, P  < 0.05), while those with urge FI had lower squeeze pressures than controls (37 cmH₂ O vs 119 cmH₂ O, P  < 0.05). Patients with urge FI had lower maximal tolerable volumes (100 mL vs 166 mL, P  < 0.05). Patients with slow-transit constipation had elevated rectal electrosensitivity thresholds compared with controls (31.4 mA vs 20.2 mA, P  < 0.05), and rectal mucosal blood flow than patients with evacuation difficulty and controls (107 vs 162 flux units (FU) [evacuation difficulty] vs 169 FU [controls], P  < 0.05). Only patients with passive FI were associated with reflex abnormalities (prolonged recovery phase (1.2 ms vs 0.5 ms, P  < 0.05) and total duration of reflex (6.3 ms vs 4.3 ms, P  < 0.05).

Anorectal motor, sensory and reflex abnormalities are seen in distinct patterns in patients with FI and constipation. This would suggest distinct physiological differences that may predict the potential for different neuromodulation treatment and behavioral modalities in these conditions.