**Question:** A young girl presents with abdominal pain and a recent change in bowel habit, with passage of mucus in stool. There is no associated blood in stool and symptoms are increased with stress. The most likely diagnosis is.

A. Irritable Bowel Syndrome (IBS)
B. Crohn's Disease
C. Ulcerative Colitis
D. Diverticulitis

**Correct Answer:** D. Diverticulitis

**Core Concept:**

Irritable bowel syndrome (IBS), Crohn's disease (CD), ulcerative colitis (UC), and diverticulitis are common gastrointestinal disorders presenting with abdominal pain, change in bowel habit, and mucus in stool. However, the specific mechanism and clinical features help differentiate these conditions.

**Why the Correct Answer is Right:**

Diverticulitis is the correct answer in this scenario because the patient has symptoms of abdominal pain, mucus in stool, and no blood in the stool. Additionally, the symptoms are aggravated with stress. The presence of mucus in stool is more commonly associated with diverticular disease rather than IBS, CD, or UC.

**Why Each Wrong Option is Incorrect:**

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by abdominal pain, altered bowel habits, and altered stool consistency. However, the presence of mucus in stool is less common in IBS compared to diverticulitis.

Crohn's disease (CD) is an inflammatory bowel disease (IBD) affecting the entire gastrointestinal tract, leading to symptoms like abdominal pain, diarrhea, and weight loss. Mucus in stool is less common in CD, as it often presents with bloody diarrhea, abdominal pain, and weight loss.

Ulcerative colitis (UC) is another IBD causing inflammation of the colon, resulting in symptoms like abdominal pain, diarrhea, and weight loss. Unlike diverticulitis, UC is not typically associated with mucus in stool.

**Clinical Pearl:**

In clinical practice, a combination of abdominal pain, mucus in stool, and stress sensitivity should raise suspicion for diverticulitis, particularly when associated with other gastrointestinal symptoms like abdominal pain and diarrhoea. However, the presence of mucus in stool does not exclude IBS or CD as a diagnosis, as these conditions can also present with mucus in stool. A thorough clinical evaluation, including a detailed medical history, physical examination, and necessary investigations, is crucial to confirm the diagnosis and guide treatment for the patient.