Inflammatory bowel disease

	Ulcerative colitis	Crohn disease
Location	Pancolitis (30%) Proctosigmoiditis (50%) Includes PSC (5%)	Terminal ileum (80%) Ileocolonic (50%) Isolated ileal (30%) Isolated colonic (20%)
Distribution	Continuous from rectum	Skip lesions, often rectum-sparing
Histology	Mucosal inflammation without granulomas	Transmural inflammation, granulomas, cobblestone
Serology	p-ANCA	Anti-Saccharomyces cervisiae IgG
Complications	Toxic megacolon Colorectal cancer	Intraabdominal abscess, perforation, fistulae, strictures, perianal disease, obstruction, colorectal cancer

Extraintestinal Manifestations

• MSK
  • Seronegative spondyloarthritis
  • Osteopenia
• Dermatologic
  • Erythema nodosum
  • Pyoderma gangrenosum
• Opthalmologic
  • Episcleritis
  • Uveitis
• Clubbing
• Renal
  • Kidney stones
• Hepatobiliary
  • Gallstones
  • Primary sclerosing cholangitis
• Hematologic
  • DVT
  • Amyloidosis
  • Anemia (iron-deficiency, chronic inflammatory, B12 deficiency)
• Aphthous ulcers

Arthritis

Type 1: Pauciarticular

• <5 joints
• Large joints
• Short duration
• Correlates with disease activity

Type 2: Polyarticular

• >5 joints
• Small joints
• Months to years
• Independent of disease activity

Differential Diagnosis

Colitis or Ileitis

• Bacterial: Shigella, enterohemorrhagic Escherichia coli, enteroinvasive Escherichia coli, Campylobacter jejuni, Salmonella, Yersinia enterocolitica, Mycobacterium tuberculosis, Clostridioides difficile, Vibrio parahaemolyticus, Chlamydia trachomatis (lymphogranuloma venereum)
• Parasitic: Entamoeba histolytica, Schistosoma, Balantidium coli, Trichinella spiralis
• Viruses: cytomegalovirus

Proctitis

• Neisseria gonorrhoeae
• Herpes simplex virus
• Chlamydia trachomatis
• Treponema pallidum
• Cytomegalovirus