Inflammatory bowel diseases

IBD Overview - The Gut's Civil War

• Chronic, relapsing autoimmune inflammation of the GI tract due to a dysregulated immune response to gut flora in genetically susceptible hosts.
• Presents with a bimodal age distribution: peaks at 15-30 years and 60-80 years.
• Key symptoms: chronic diarrhea (may be bloody), abdominal pain, fever, weight loss.
• Associated with numerous extraintestinal manifestations (EIMs), such as arthritis, uveitis, and skin lesions.

⭐ Smoking is protective in Ulcerative Colitis but is a risk factor for Crohn's Disease.

Crohn's Disease - Cobblestones & Skips

• Pathology: Transmural, full-thickness inflammation leading to fistulas & strictures. Features non-caseating granulomas in ~50% of cases.
• Distribution: Affects any part of the GI tract ("gum to bum"), often the terminal ileum. Characterized by "skip lesions" (healthy tissue between diseased areas) and frequent rectal sparing.
• Appearance: Linear ulcers, fissures, and a classic "cobblestone" mucosa.
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• 📌 Mnemonic: A Crohn's GRANny SKIPs down a COBBLESTONE road (Granulomas, Skip lesions, Cobblestone mucosa).

⭐ High-Yield: Strongly associated with Anti-Saccharomyces cerevisiae antibodies (ASCA).

Ulcerative Colitis - Bloody & Continuous

• Patho: Continuous mucosal & submucosal inflammation. Always involves the rectum, extending proximally. Loss of haustra leads to "lead pipe" sign on imaging.
• Gross/Endo: Friable, erythematous mucosa with bleeding and pseudopolyps; no skip lesions.
• Histo: Crypt abscesses, branching crypts, and a diffuse inflammatory infiltrate. No granulomas.
• Clinical: Hallmark is bloody diarrhea, with tenesmus and lower abdominal pain.
• Complications: Toxic megacolon, hemorrhage, ↑ colorectal cancer risk after 8-10 yrs.

⭐ Association: Strongly associated with Primary Sclerosing Cholangitis (PSC); p-ANCA is positive in ~70% of patients.

IBD Complications - Beyond the Bowel

• Musculoskeletal (Most Common)
  • Peripheral arthritis: Asymmetric, migratory, parallels IBD activity.
  • Axial arthropathy: Sacroiliitis & ankylosing spondylitis (HLA-B27+), independent of IBD activity.
• Dermatologic
  • Erythema nodosum: Painful nodules on shins; mirrors Crohn's activity.
  • Pyoderma gangrenosum: Deep, necrotic ulcers; often with UC.
• Ocular: Uveitis, episcleritis, scleritis.
• Hepatobiliary

  ⭐ Primary Sclerosing Cholangitis (PSC) is strongly associated with Ulcerative Colitis, carrying a high risk for cholangiocarcinoma. Look for ↑ALP & p-ANCA.

IBD Management - Cooling the Flames

• Aminosalicylates (5-ASA): For mild-to-moderate disease, particularly UC. Mainstay of maintenance.
• Corticosteroids: Used for inducing remission during acute, moderate-to-severe flares. Not for long-term use.
• Immunomodulators (Azathioprine, 6-MP): Steroid-sparing agents for maintenance.
• Biologics (TNF-α inhibitors): For moderate-to-severe disease refractory to other therapies.

⭐ Always screen for latent TB before initiating TNF-α inhibitors due to the risk of reactivation.

High‑Yield Points - ⚡ Biggest Takeaways

• Crohn's disease has transmural inflammation, skip lesions, and non-caseating granulomas, affecting any part of the GI tract.
• Ulcerative colitis involves continuous mucosal inflammation limited to the colon, with crypt abscesses and bloody diarrhea.
• Key signs: "Cobblestone" mucosa and fistulas in Crohn's; pseudopolyps and toxic megacolon in UC.
• Smoking worsens Crohn's but is paradoxically protective in UC.
• Both carry a risk of colorectal cancer and extraintestinal manifestations like arthritis and uveitis.