Crohn disease

Ulcerative colitis is a chronic immune-mediated disease of continuous mucosal inflammation that begins in the rectum and extends proximally through the colon, presenting with bloody diarrhea and tenesmus and confirmed by colonoscopy with biopsy. Treatment is stepped by extent and severity from 5-aminosalicylates through corticosteroids, immunomodulators, and biologics, with acute severe disease requiring IV corticosteroids and medical or surgical rescue, and colectomy remains curative.

Colorectal cancer is an adenocarcinoma that arises through the adenoma-carcinoma sequence and presents differently by location, with right-sided tumors causing occult bleeding and iron-deficiency anemia and left-sided tumors causing obstruction and hematochezia. Colonoscopy with biopsy confirms the diagnosis, TNM staging on CT chest/abdomen/pelvis with CEA guides treatment, and management ranges from surgical resection alone for localized disease to adjuvant FOLFOX for node-positive colon cancer, neoadjuvant chemoradiation for rectal cancer, and molecularly targeted systemic therapy for metastatic disease.

Primary sclerosing cholangitis is an autoimmune fibroinflammatory disease of the large bile ducts, occurring mostly in young men and associated with inflammatory bowel disease, chiefly ulcerative colitis, in 80 to 90% of cases. MRCP showing multifocal strictures and dilations confirms the diagnosis, no drug alters progression, and management centers on endoscopic dilation of dominant strictures, surveillance for cholangiocarcinoma and colorectal cancer, and liver transplantation for advanced disease.

Celiac disease is an immune-mediated small-intestinal enteropathy triggered by dietary gluten in genetically predisposed individuals, presenting with malabsorptive diarrhea, iron-deficiency anemia, or dermatitis herpetiformis. Diagnosis requires IgA tissue transglutaminase serology with a total IgA level while the patient still eats gluten, confirmed by duodenal biopsy showing villous atrophy, and the only treatment is a strict lifelong gluten-free diet.

Irritable bowel syndrome is a functional disorder of gut-brain interaction diagnosed clinically by Rome IV criteria, recurrent abdominal pain related to defecation, stool frequency, or stool form, without alarm features. Management is subtyped by stool pattern, with fiber and dietary change first, then IBS-C secretagogues or IBS-D antidiarrheals and antibiotics, and low-dose tricyclics or antispasmodics for pain.

Ischemic colitis is the most common form of gastrointestinal ischemia, caused by a nonocclusive low-flow state in colonic microvessels that classically injures the watershed splenic flexure and rectosigmoid junction. Most cases are mild and self-limited with supportive care, but segmental CT thickening with peritoneal signs, pneumatosis, or gangrene demands emergent surgery rather than antibiotics alone.

Diverticulitis is inflammation and micro- or macro-perforation of a colonic diverticulum, most often sigmoid, presenting with left lower quadrant pain, fever, and altered bowel habits. CT abdomen and pelvis with contrast confirms the diagnosis, separates uncomplicated from complicated disease, and grades complicated disease by the modified Hinchey classification to guide antibiotics, drainage, or surgery.

Microscopic colitis is a cause of chronic watery, non-bloody diarrhea in older women with a grossly normal colonoscopy, diagnosed only by random colon biopsy showing lymphocytic or collagenous histology. Management starts with stopping culprit drugs and antidiarrheals, then oral budesonide for induction and, if needed, maintenance.