Inflammatory Bowel Disease

IBD Overview - Gut Feeling Gone Wrong

• Definition: Chronic, relapsing inflammatory disorders of the gastrointestinal tract (GIT).
• Epidemiology:
  • Bimodal age distribution: Peaks at 15-30 years and 50-80 years.
  • Rising incidence globally, including a significant increase in India.
• Etiology (Multifactorial):
  • Genetic predisposition: Key genes like NOD2/CARD15.
  • Immune dysregulation: Aberrant immune response to gut flora.
  • Gut microbiota: Dysbiosis, reduced diversity.
  • Environmental triggers: Smoking (complex role: ↑Crohn's, ↓UC), diet, NSAIDs, infections.

⭐ The 'hygiene hypothesis' posits that decreased early-life microbial exposure might elevate IBD susceptibility.

Crohn's Disease - Skip & Strike

• Distribution: Any part of GIT ('gum to bum'); terminal ileum, colon typical.
• Pattern: Skip lesions (discontinuous).
• Inflammation: Transmural (full thickness).
  • Linear ulcers, cobblestone appearance.
  • Creeping fat (mesenteric fat wrapping bowel).
• Complications: Fistulae, strictures, abscesses.
• Microscopy: Non-caseating granulomas (pathognomonic, not always present).
• Pathogenesis: Th1/Th17 mediated immune response. 📌 Mnemonic: 'A Christmas GRANdma SKIPped over FAT COBBLEd WALLS from her MOUTH to her ANUS' (Crohn's, Granulomas, Skip lesions, Fat (creeping), Cobblestone, Transmural, Mouth to Anus involvement).

⭐ Smoking is a significant risk factor for Crohn's disease and worsens its course.

Ulcerative Colitis - Continuous Chaos

• Limited to colon & rectum; continuous inflammation starting from rectum, extends proximally.
• 📌 CLOSEUP: Continuous, Limited to colon/rectum, Only mucosa/submucosa, Smoking protective, Extends proximally, Ulcers (superficial, broad-based), Pseudopolyps/p-ANCA.
• Pathology:
  • Gross: Diffuse erythema, friability, pseudopolyps.
  • Micro: Mucosal & submucosal inflammation ONLY; crypt abscesses, crypt distortion, goblet cell depletion.
• Immune: Th2 mediated (less clear-cut than CD).

⭐ p-ANCA (perinuclear anti-neutrophil cytoplasmic antibodies) are positive in about 60-70% of Ulcerative Colitis patients.

IBD Comparison & Diagnosis - Telling Them Apart

• Imaging: CT/MR Enterography (evaluates extent/complications, esp. CD). Barium studies (less common).
• Stool Studies: Fecal calprotectin (monitors activity).

⭐ While ASCA is more common in Crohn's and p-ANCA in UC, their sensitivity and specificity are not absolute for diagnosis.

Complications & EIMs - Beyond the Bowel

Intestinal Complications:

• Crohn's Disease (CD): Fistulas, Strictures, Abscesses, Malabsorption, Perforation.
• Ulcerative Colitis (UC): Toxic megacolon, Severe hemorrhage, Perforation, ↑ Dysplasia/Colorectal Cancer (CRC) risk (esp. pancolitis >8-10 yrs).

Extra-intestinal Manifestations (EIMs): 📌 Mnemonic: A PIE SAC

• Arthritis (peripheral, ankylosing spondylitis)
• Pyoderma gangrenosum
• Iritis/Uveitis, Episcleritis
• Erythema nodosum
• Sclerosing cholangitis (Primary, strongly assoc. with UC)
• Aphthous stomatitis
• (Other EIMs: Osteoporosis, Clubbing)

⭐ Primary Sclerosing Cholangitis (PSC) is seen in about 5% of UC patients and significantly increases the risk of cholangiocarcinoma and colorectal cancer.

High‑Yield Points - ⚡ Biggest Takeaways

• Crohn's Disease: Transmural inflammation, skip lesions, non-caseating granulomas, cobblestone mucosa. Fistulas and strictures common.
• Ulcerative Colitis: Continuous mucosal/submucosal inflammation starting in rectum. Crypt abscesses, pseudopolyps, and bloody diarrhea are characteristic.
• Key Complications: Crohn's: malabsorption, fistulae. UC: toxic megacolon, significantly ↑ colorectal cancer risk.
• Associations: Crohn's: ASCA positive, smoking worsens. UC: p-ANCA positive, smoking is protective, PSC association.
• Shared Extraintestinal: Both can present with arthritis, uveitis, and erythema nodosum.