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Inflammatory Bowel Disease (IBD) is a group of chronic, relapsing–remitting inflammatory disorders of the gastrointestinal (GI) tract, primarily comprising:

Ulcerative Colitis (UC): Confined to the colon and rectum, affecting the mucosa and submucosa.
Crohn’s Disease (CD): Can involve any part of the GI tract, from mouth to anus, with transmural inflammation and skip lesions. </aside>

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https://youtu.be/4lzfvwCPsKw

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Etiopathogenesis

IBD is multifactorial, involving:

Genetic predisposition (e.g., NOD2/CARD15 mutations in Crohn’s)
Immune dysregulation (Th1/Th17 in Crohn’s; Th2-like in UC)
Environmental triggers (diet, smoking, stress)
Gut microbiota imbalance (dysbiosis)

![Macroscopic and microscopic changes after a long-standing activity of ulcerative colitis and Crohn’s disease; the histological features that define chronicity are crypt architectural distortion, crypt atrophy, non-necrotizing granulomas, basal plasmacytosis, basally located lymphoid aggregates, and Paneth cell metaplasia; the presence of neutrophils defines inflammatory activity.

Jucan AE, Gavrilescu O, Dranga M, Popa IV, Mihai I-R, Mihai V-C, Stefanescu G, Drug VL, Prelipcean CC, Vulpoi R-A, et al. Evaluation of Disease Activity in Inflammatory Bowel Disease: Diagnostic Tools in the Assessment of Histological Healing. Biomedicines. 2023; 11(11):3090. https://doi.org/10.3390/biomedicines11113090](attachment:aeb4d0c2-5a33-4f43-a76d-d675d6578749:biomedicines-11-03090-g001.png)

Macroscopic and microscopic changes after a long-standing activity of ulcerative colitis and Crohn’s disease; the histological features that define chronicity are crypt architectural distortion, crypt atrophy, non-necrotizing granulomas, basal plasmacytosis, basally located lymphoid aggregates, and Paneth cell metaplasia; the presence of neutrophils defines inflammatory activity.

Clinical Features

Feature	Ulcerative Colitis	Crohn’s Disease
Site	Colon (always involves rectum)	Mouth to anus (ileum most common)
Pain	Lower left abdomen	Right lower abdomen (ileocecal)
Diarrhea	Bloody, mucous-laden	Watery or steatorrhea
Weight loss	Mild to moderate	Significant
Fistulas, strictures	Rare	Common

Pattern of involvement:

![Different types of Inflammatory Bowel diseases. (A) Ulcerative colitis: proctitis, left-sided colitis, and extended colitis; (B) Crohn’s disease: Ileocecal Crohn’s disease, Crohn’s colitis, and Fistulising Crohn’s disease. Red indicates area of inflammation.

Burke, K.E., D’Amato, M., Ng, S.C. et al. Microscopic colitis. Nat Rev Dis Primers 7, 39 (2021). https://doi.org/10.1038/s41572-021-00273-2](attachment:248b74f0-4732-4539-8e2c-0b5e36dbbcce:jcm-09-01273-g001.png)

Different types of Inflammatory Bowel diseases. (A) Ulcerative colitis: proctitis, left-sided colitis, and extended colitis; (B) Crohn’s disease: Ileocecal Crohn’s disease, Crohn’s colitis, and Fistulising Crohn’s disease. Red indicates area of inflammation.

Burke, K.E., D’Amato, M., Ng, S.C. et al. Microscopic colitis. Nat Rev Dis Primers 7, 39 (2021). https://doi.org/10.1038/s41572-021-00273-2