BACKGROUND: Defecation dysfunction may contribute to chronic constipation (CC), but the impact of obesity on anorectal physiology in CC remains unclear. We aimed to evaluate the relationship between obesity and anorectal function on physiologic testing in patients presenting with CC.

METHODS: This was a retrospective cohort study of consecutive adults who underwent high resolution anorectal manometry (HRAM) at a tertiary center for CC. Patient demographics, clinical history, surgical/obstetric history, medications, and HRAM results were reviewed. Patients were classified into obese (BMI > 30 kg/m2) vs non-obese (BMI < 30 kg/m2) groups at the time of HRAM. Fisher-exact/student t-test for univariate analyses and general linear regression for multivariable analysis were performed.

RESULTS: 383 adults (mean 50.3 years; 85.8% female) with CC were included. On HRAM, patients with obesity had lower anal sphincter resting tone (37.3 vs 48.5 mmHg, p = 0.005) and maximum squeeze pressure (104.8 mmHg vs 120.0 mmHg, p = 0.043). No significant differences in dyssynergia (61% vs 53%, p = 0.294) and failed balloon expulsion (18% vs 25%, p = 0.381) were found between obese and non-obese groups. On balloon distention testing, the maximum tolerated (163.5 vs 147.6 mL, p = 0.042) and urge sensation (113.9 vs 103.7 mL, p = 0.048) volumes were significantly increased among patients with obesity. After adjusting for potential confounders, obesity remained independently associated with increased maximum tolerated volume (β-coefficient 13.7, p = 0.049).

CONCLUSION: Obesity was independently associated with altered rectal sensitivity among patients with CC. Altered rectal sensation may play an important role in CC among patients with obesity. Anorectal physiology testing should be considered to understand the pathophysiology and guide management.