True about Crohn disease are all EXCEPT?
**Core Concept**
Crohn's disease is a type of inflammatory bowel disease (IBD) characterized by chronic inflammation and damage to the gastrointestinal tract, often involving the terminal ileum and colon. It is a complex condition involving immune system dysregulation, genetic predisposition, and environmental factors.
**Why the Correct Answer is Right**
Crohn's disease is a transmural disease, meaning it affects all layers of the gastrointestinal wall. This is in contrast to ulcerative colitis, which primarily affects the mucosa. The pathophysiology of Crohn's disease involves an abnormal immune response to luminal antigens, leading to activation of T cells and production of pro-inflammatory cytokines. This results in chronic inflammation, ulceration, and fibrosis.
**Why Each Wrong Option is Incorrect**
**Option A:** Crohn's disease is indeed more common in individuals with a family history of the disease, with a significant genetic component.
**Option B:** Crohn's disease is associated with an increased risk of colorectal cancer, particularly in patients with long-standing disease.
**Option C:** Crohn's disease can affect any part of the gastrointestinal tract, from the mouth to the anus, but it most commonly affects the terminal ileum and colon.
**Clinical Pearl / High-Yield Fact**
It's essential to distinguish between Crohn's disease and ulcerative colitis, as the treatment and prognosis differ significantly between the two conditions. A key clinical clue is the presence of skip lesions, which are areas of diseased bowel interspersed with normal bowel, a hallmark of Crohn's disease.
**Correct Answer: D.**