Colonic response to laxative ingestion as assessed by MRI differs in constipated irritable bowel syndrome compared to functional constipation

Background Functional constipation ( FC ) and irritable bowel syndrome with constipation ( IBS ‐C) share many symptoms but underlying mechanisms may be different. We have developed a magnetic resonance imaging ( MRI ) technique to measure intestinal volumes, transit, and motility in response to a laxative, Moviprep ® . We aim to use these biomarkers to study the pathophysiology in IBS ‐C and FC . Methods Twenty‐four FC and 24 IBS ‐C were studied. Transit was assessed using the weighted average position score ( WAPS ) of five MRI marker pills, taken 24 h before MRI scanning. Following baseline scan, participants ingested 1 L of Moviprep ® followed by hourly scans. Magnetic resonance imaging parameters and bowel symptoms were scored from 0 to 4 h. Key Results Weighted average position score for FC was 3.6 (2.5–4.2), significantly greater than IBS ‐C at 2.0 (1.5–3.2), p = 0.01, indicating slower transit for FC. Functional constipation showed greater fasting small bowel water content, 83 (63–142) mL vs 39 (15–70) mL in IBS ‐C, p < 0.01 and greater ascending colon volume ( AC ), 314 (101) mL vs 226 (71) mL in IBS ‐C, p < 0.01. FC motility index was lower at 0.055 (0.044) compared to IBS ‐C, 0.107 (0.070), p < 0.01. Time to first bowel movement following ingestion of Moviprep ® was greater for FC , being 295 (116–526) min, compared to IBS ‐C at 84 (49–111) min, p < 0.01, and correlated with AC volume 2 h after Moviprep ® , r = 0.44, p < 0.01. Using a cut‐off >230 min distinguishes FC from IBS ‐C with low sensitivity of 55% but high specificity of 95%. Conclusion & Inferences Our objective MRI biomarkers allow a distinction between FC and IBS ‐C.