Chronic Bowel Disorders: Introduction

IBS-C, or constipation-predominant IBS, is characterized by reduced bowel movement frequency. IBS-D, or diarrhea-predominant IBS, involves recurrent abdominal discomfort and frequent loose stools. Both manifest chronic abdominal pain but differ in bowel habit patterns and require distinct treatment approaches for symptom management.

Ulcerative colitis causes continuous mucosal inflammation limited to the rectum and colon. Crohn's disease features discontinuous transmural inflammation affecting the entire digestive tract, with the terminal ileum most commonly involved. Transmural inflammation in Crohn's damages all intestinal layers, potentially causing fibrosis, strictures, or fistulas.

IBD involves an abnormal immune response to gut microbiota in genetically predisposed individuals. Ulcerative colitis exhibits TH2 and TH17-mediated inflammation with lymphocytic and neutrophilic infiltrates. Crohn's disease shows TH1-mediated inflammation with elevated IL-12, IL-23, IFN-γ, and TNF-α levels, causing macrophage and lymphocyte infiltration.

IBS pathophysiology involves visceral motor and sensory dysfunction linked to the gut-brain axis, connecting gastrointestinal function with mood and stress. Heightened visceral sensitivity in IBS responds to both normal physiological stimuli and harmful stimuli, with psychological stress amplifying symptom severity. This complex interplay requires dietary, stress management, and drug therapy.

IBD can lead to extraintestinal manifestations involving joints, skin, or eyes, and increases colorectal cancer risk. Crohn's disease may develop fibrosis, strictures, or fistulas from transmural inflammation. Ulcerative colitis can rarely progress to primary sclerosing cholangitis, causing inflammation and fibrostenosis of the biliary tree.

Medical treatment for IBD aims to suppress the inflammatory response, achieve mucosal healing, and maintain remission. Specific complications such as fistulas require targeted intervention. Treatment strategies vary based on disease subtype and severity, with drugs for treatment of Crohn's disease in IBD using biologic agents anti TNF and other approaches available.

IBS involves visceral motor and sensory dysfunction with heightened sensitivity to normal and harmful stimuli, often linked to mood disorders and the gut-brain axis. IBD involves chronic intestinal inflammation from immune attacks on gut bacteria, causing structural damage. IBS lacks the immune-mediated inflammation and tissue damage characteristic of IBD.