Inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic immune-mediated inflammatory disease of the gastrointestinal tract, encompassing Crohn's disease and ulcerative colitis. | Feature | Crohn disease | Ulcerative colitis | | --- | --- | --- | | Location | Any GI segment (esp. terminal ileum & colon) | Colon and rectum only (starts at rectum, continuous) | | Pattern | Skip lesions (patchy inflammation) | Continuous (always includes rectum) | | Depth of inflammation | Transmural (full-thickness) | Mucosal (colon lining only) | | Histology | Noncaseating granulomas (33% of cases) | Crypt abscesses, no granulomas | | Endoscopy | Cobblestoning, strictures, skip areas | Friability, pseudopolyps, continuous ulcers | | Extraintestinal | Fistulas, strictures, perianal disease common | Primary sclerosing cholangitis, toxic megacolon |

• Affects mostly young adults in North America/Europe (15–30 yrs), with relapsing-remitting GI symptoms. IBD is lifelong (no cure) and increases morbidity: e.g. strictures, fistulas, colorectal cancer (CRC) risk. Treatment (meds, surgery) is complex and high-yield for exams (flares, complications, EIM).

• Recurrent diarrhea (often bloody in UC), abdominal pain (Crohn—RLQ, UC—LLQ/tenesmus), weight loss, and systemic symptoms (fever, fatigue).
• Extraintestinal manifestations are common (10–30%): e.g. arthritis, uveitis, erythema nodosum, pyoderma gangrenosum, primary sclerosing cholangitis (PSC, UC>CD).
• Cigarette smoking worsens Crohn but may improve UC. Family history in ~10-25% of patients (genetic predisposition).
• Complications include malabsorption (more in Crohn), fistulas/abscesses (Crohn), toxic megacolon and colon cancer risk (UC).

1. Mild-to-moderate UC: 5-aminosalicylates (mesalamine, sulfasalazine) oral or topical for induction and maintenance.
2. Crohn with ileal involvement: budesonide (steroid) for mild disease, or 5-ASA (limited benefit) for colonic disease.
3. Moderate-severe flares (UC or Crohn): systemic corticosteroids (prednisone) for induction (taper in ~8 wk).
4. Maintenance: immunomodulators (azathioprine, 6-MP, methotrexate) and/or biologics (anti-TNF: infliximab, adalimumab; anti-integrin: vedolizumab; anti-IL12/23: ustekinumab; JAK inhibitor tofacitinib for UC).
5. Antibiotics (metronidazole, ciprofloxacin) for perianal Crohn or abscesses.
6. Surgery: colectomy cures UC (indications: refractory disease, dysplasia, toxic megacolon); Crohn surgeries (resection, strictureplasty) for complications, not curative (disease often recurs).

• Think continuous (UC) vs skip lesions (Crohn); rectum always involved in UC, often spared in Crohn.
• UC: limited to colon mucosa (crypt abscesses, pseudopolyps); Crohn: any GI segment, transmural (cobblestoning, strictures).
• Noncaseating granulomas favor Crohn (supportive finding).
• Extrahepatic cholangitis (PSC) and higher CRC risk mainly in UC.
• Smoking: increases Crohn risk/severity, but is protective in UC.

• Toxic megacolon: acute colonic dilation with systemic toxicity (fever, tachycardia) – emergency surgery.
• Fulminant colitis: severe UC unresponsive to therapy (high leukocytosis, fever) – colectomy needed.
• Colon cancer risk: long-standing extensive colitis (surveillance colonoscopy starting ~8–10 years after diagnosis).
• Perianal disease: fistulas, abscesses common in Crohn (up to 50% of patients).
• Stricture/obstruction: small-bowel strictures in Crohn may cause obstruction requiring surgery.

1. Suspect IBD in a patient with chronic diarrhea/abdominal pain: check inflammation markers (CRP, ESR) and stool studies (rule out infection, test fecal calprotectin).
2. Perform colonoscopy with biopsy for diagnosis (full colonoscopy if possible; sigmoidoscopy if fulminant).
3. Differentiate UC vs Crohn: UC = continuous colonic mucosal disease (rectum involved); Crohn = any GI (skip lesions, transmural, possible granulomas).
4. If Crohn suspected and colonoscopy inconclusive, do imaging (CT/MRI enterography) or capsule endoscopy for small bowel disease.
5. Treat based on severity: mild UC → aminosalicylates; mild Crohn → budesonide; moderate/severe → add corticosteroids (induction), then immunomodulators or biologics for maintenance.
6. Reassess response: if refractory or complicated (fistula, abscess, strictures), escalate therapy or consult surgery (e.g. colectomy in UC, resection in Crohn).

• A 25-year-old with crampy RLQ pain, chronic nonbloody diarrhea, and weight loss; colonoscopy shows aphthous ulcers and skip lesions with biopsy demonstrating granulomas → Crohn disease.
• A 30-year-old with 8-week history of bloody diarrhea and tenesmus; colonoscopy shows continuous erythema and ulcers from rectum proximally, biopsy shows crypt abscesses → Ulcerative colitis.