Abnormal accumulation of intestinal fluid following ingestion of an unabsorbable carbohydrate in patients with irritable bowel syndrome: an MRI study

BackgroundPostprandial discomfort following intake of poorly absorbable, but fermentable carbohydrates is a common complaint in patients with irritable bowel syndrome (IBS). We used lactulose as a model substance for this group of symptom triggering carbohydrates, aiming to visualize the intestinal response in IBS patients compared to healthy controls. MethodsPatients with IBS according to Rome III criteria (n=52) and healthy controls (n=16) underwent a lactulose challenge test. By using magnetic resonance imaging, we measured small bowel water content (SBWC), and distension (diameter) of the distal ileum and the colon, both in fasting state and 1h after ingestion of 10g lactulose. We recorded symptoms after lactulose ingestion. Key ResultsLactulose provoked significantly more symptoms in IBS patients than in healthy controls (p<0.0001). SBWC increased more in the patient group compared to the control group (p=0.0005). The postprandial diameter of the terminal ileum was larger in patients with IBS and the postprandial diameter of the ascending colon was smaller in patients with diarrhea-predominant phenotype (IBS-D). Symptoms were not correlated with change in SBWC (r=0.05; p=0.11), nor to the diameters of the terminal ileum or the colon. Conclusions & InferencesCompared to healthy controls, IBS patients developed more symptoms and had an abnormal accumulation of fluid in the small bowel in response to ingestion of the unabsorbable carbohydrate lactulose. This may be due to impaired motor activity of the small intestine or impaired function of the ileocecal segment.