**Question:** A patient presents with history of mild diarrhea, blood in stools with multiple fistulas. What is the most probable diagnosis: September 2007

**Core Concept:** Inflammatory bowel diseases (IBD) are a group of chronic, relapsing, and remitting conditions affecting the gastrointestinal tract. Two main types of IBD are Crohn's disease and ulcerative colitis. Crohn's disease typically involves any part of the gastrointestinal tract from the mouth to the anus, whereas ulcerative colitis is limited to the colon and rectum. Both conditions can present with symptoms like diarrhea, blood in stools, and sometimes fistulas.

**Why the Correct Answer is Right:** The correct answer is **D**. The presence of blood in stools and multiple fistulas are strong indicators of Crohn's disease. In contrast to ulcerative colitis, which typically manifests as bloody diarrhea limited to the colon and rectum, Crohn's disease can involve any part of the gastrointestinal tract from the mouth to the anus. Furthermore, fistulas are more common in Crohn's disease, as opposed to ulcerative colitis.

**Why Each Wrong Option is Incorrect:**

A. While ulcerative colitis can present with bloody diarrhea and fistulas, the involvement of the entire gastrointestinal tract from the mouth to the anus makes Crohn's disease a more probable diagnosis. Ulcerative colitis's limited involvement in the colon and rectum rules out this option.

B. Blood in stools and fistulas can be seen in both Crohn's disease and ulcerative colitis. However, the involvement of the entire gastrointestinal tract in Crohn's disease makes it more likely than ulcerative colitis, which is limited to the colon and rectum.

C. While bloody diarrhea and fistulas can occur in both Crohn's disease and ulcerative colitis, the involvement of the entire gastrointestinal tract in Crohn's disease makes it more likely than ulcerative colitis, which is limited to the colon and rectum.

D. The combination of bloody diarrhea, fistulas, and involvement of the entire gastrointestinal tract make Crohn's disease a more probable diagnosis than ulcerative colitis, which is limited to the colon and rectum.

**Clinical Pearl:** Fistulas in Crohn's disease are often transmural, meaning they involve the full thickness of the intestinal wall, as opposed to submucosal fistulas in ulcerative colitis. This transmural fistulas in Crohn's disease contribute to the diagnosis and differentiate it from ulcerative colitis.