Inflammatory and Functional Bowel Disorders
Core concepts
Distinguish inflammatory bowel disease subtypes and functional disorders. Ulcerative colitis is continuous, starts in the rectum, and involves mucosa; Crohn disease is transmural, skip lesions, and can affect any segment with fistulas and strictures. Extraintestinal manifestations include pyoderma gangrenosum, erythema nodosum, and primary sclerosing cholangitis (more with UC). Treat mild-to-moderate UC with mesalamine; steroids induce but do not maintain remission; biologics and immunomodulators serve moderate-to-severe disease.
Irritable bowel syndrome is a functional disorder diagnosed by symptom criteria with alarm features excluded. Rome criteria plus absence of alarm features (weight loss, bleeding, anemia, nocturnal symptoms, family history) allow diagnosis without exhaustive testing. Celiac serology is a reasonable screen. Microscopic colitis causes chronic watery diarrhea, often with NSAID or PPI exposure.
Traps
Do not use steroids for maintenance. Questions test that toxic megacolon and fulminant colitis require urgent evaluation and avoiding antimotility agents. Distinguish IBS from IBD: IBS lacks inflammation and bleeding. Check that Crohn perianal disease may need imaging before surgery.
Rule of thumb
In chronic watery diarrhea with normal colonoscopy, biopsy the colon to look for microscopic colitis before labeling it IBS.