Chronic bowel diseases are a group of long-term conditions affecting the digestive tract, characterized by inflammation and damage to the gut lining. These conditions primarily include irritable bowel syndrome and inflammatory bowel disease.

Irritable Bowel Syndrome (IBS) is a common disorder affecting the gastrointestinal tract. The distinctive feature is recurrent abdominal pain associated with altered bowel movements, manifesting as constipation, diarrhea, or fluctuating between both. The heightened visceral sensitivity in IBS is observed in response to both physiological (e.g., normal bowel movements or gas) and harmful stimuli, with psychological factors often influencing symptom severity due to their connection with the gut-brain axis. As a result, its pathophysiology involves a complex interplay of visceral motor and sensory dysfunction, often linked with mood disorders. IBS patients require dietary and stress management alongside drug therapy.

Inflammatory bowel disease (IBD) encompasses chronic intestinal conditions, typically categorized as ulcerative colitis and Crohn's disease. Both subtypes are characterized by an abnormal immune response to gut microbiota in genetically predisposed individuals.

Ulcerative colitis manifests through continuous mucosal inflammation of the colon, extending from the rectum to varying extents. It involves superficial lesions with lymphocytic and neutrophilic infiltrates, reflecting an immune response mediated primarily by TH2 and TH17 pathways.

Crohn's disease features transmural inflammation that can affect any part of the gastrointestinal tract, predominantly near the ileocecal valve. The inflammation is not always continuous, resulting in alternative inflamed and normal mucosa patches. The transmural inflammation, which damages all layers of the intestinal epithelium, can lead to fibrosis, strictures, or the formation of fistulas. The lesions exhibit significant lymphocyte and macrophage infiltration at the cellular level, causing submucosal fibrosis. The cytokine profile indicates a TH1-mediated inflammatory process with increased IL-12, IL-23, IFN-γ, and TNF-α levels.

Both diseases are associated with extraintestinal manifestations involving the joints, skin, or eyes, and can increase the risk of colorectal cancer. Primary sclerosing cholangitis, a severe but rare complication, can occur in cases of ulcerative colitis, leading to inflammation and fibrostenosis of the intra- and extrahepatic biliary tree.

Medical treatment for IBD aims to suppress the inflammatory response, achieve mucosal healing, maintain remission, and treat specific complications such as fistulas.