Abnormal anorectal manometric and sensory functions in patients with functional anorectal pain

High-resolution anorectal manometry (HARM) is widely used for diagnosis and assessment of constipation and fecal incontinence. However, limited information is available on HARM-identifiable characteristics in patients with functional anorectal pain (FARP). This study explored the pathogenesis of FARP by investigating their anorectal physiological and psychological characteristics using HARM.

140 patients with FARP who had undergone standard HARM examinations at our institution between January 2021 to January 2023, were retrospectively included for analysis. 110 controls underwent the standard HARM examinations at our institution. Pain was assessed in the FARP group using the visual analog scale (VAS) and psychological status using the Hamilton Anxiety and Depression scales.

The mean age was 53.8 ± 11.5 years (range 22-80) in the FARP group and 51.03 ± 12.11 years (range 28-75) in the control group. The mean VAS score in the FARP group was 5.57 ± 2.24. Sensation of desire to defecate, sensation of urgency to defecate, and maximum tolerable sensation were significantly lower in the FARP group, compared with the control group (P < 0.05), demonstrating rectal hypersensitivity. The residual anal canal pressure during defecation, anal resting pressure, and maximum squeeze pressure were significantly lower in the FARP group (P < 0.01 vs. controls). The anal resting pressure was positively correlated with these sensory thresholds. In addition, anxiety was detected in 63.8% and depression in 59% of patients with FARP.

The pathophysiology of FARP may involve rectal hypersensitivity and abnormal anal sphincter pressure. FARP is often accompanied by anxiety and depression. HARM may be used as a diagnostic tool for assessing pathophysiology of FARP.