Association between opioid usage and rectal dysfunction in constipation: A cross-sectional study of 2754 patients.

Background: Opioid use has reached epidemic proportions. In contrast to the known effect of opioids on gut transit, the effect on rectal sensorimotor function has not been comprehensively investigated.

Methods: Cross-sectional (hypothesis-generating) study of anorectal physiology studies in 2754 adult patients referred to a tertiary unit (2004-2016) for investigation of functional constipation (defined by "derived" Rome IV core criteria). Statistical associations between opioid usage, symptoms, and anorectal physiological variables were investigated. Opioids were sub-classified as prescriptions for mild-moderate or moderate-severe pain.

Key Results: A total of 2354 patients (85.5%) were classified as non-opioid users, 162 (5.9%) as opioid users for mild-moderate pain, and 238 (8.6%) for moderate-severe pain. Opioids for moderate-severe pain were associated with increased symptomatic severity (Cleveland Clinic constipation score 18.5 vs 15.1; mean difference 2.9 [95%-CI 2.3-3.6]; P < .001), rectal hyposensitivity (odds ratio 1.74 [95%-CI 1.23-2.46]; P = .002), functional evacuation disorders (odds ratio 1.73 [95%-CI 1.28-2.34]; P < .001), and delayed whole-gut transit (odds ratio 1.68 [95%-CI 1.19-2.37]; P = .003). Differences in anorectal variables between opioid users for mild-moderate pain and non-opioid users were not statistically significant. Hierarchical opioid use (non vs mild-moderate vs moderate-severe) was associated with decreasing proportions of patients with no physiological abnormality on testing (40.2% vs 38.1% vs 29.2%) and increasing proportions with both delayed whole-gut transit and rectal sensorimotor dysfunction (16.6% vs 17.5% vs 28.5%).

Conclusions And Inferences: Opioid use is over-represented in patients referred for investigation of constipation. Opioids for moderate-severe pain are associated with rectal sensorimotor abnormalities. Further studies are required to determine whether this association indicates causation.