**Question:** A 50-year-old male known case of ulcerative colitis presents with acute onset abdominal distention and vomiting. The next investigation would be:

A. Ulcerative colitis activity index
B. Complete blood count (CBC)
C. Abdominal X-ray
D. Abdominal ultrasound

**Correct Answer:** **D. Abdominal ultrasound**

**Core Concept:** Ulcerative colitis is a type of inflammatory bowel disease (IBD) that affects the colon. It often presents with symptoms like abdominal pain, diarrhoea, and weight loss. In severe cases, it can lead to complications such as abdominal distension and vomiting due to intestinal obstruction or perforation.

**Why the Correct Answer is Right:** In this scenario, the patient is a known case of ulcerative colitis and presents with acute abdominal distention and vomiting. Ulcerative colitis can lead to complications like intestinal obstruction due to inflammation and stricture formation. Ulcerative colitis can cause mesenteric lymphadenopathy (enlarged lymph nodes) and ascites (fluid accumulation in the peritoneal cavity), which can both be visualized using abdominal ultrasound.

**Why Each Wrong Option is Incorrect:**

A. Ulcerative colitis activity index is a scoring system to assess the severity of the disease and monitor treatment response, not a diagnostic tool for complications.
B. CBC is a general screening test for infections, not specific for complications of ulcerative colitis.
C. Abdominal X-ray might show radiological features of intestinal obstruction or pneumatosis coli (gas within the colon), but it lacks the ability to visualize mesenteric lymphadenopathy and ascites like abdominal ultrasound.

**Why the Correct Answer is Right:** Ultrasound is the appropriate diagnostic tool in this scenario because it can visualize complications like mesenteric lymphadenopathy and ascites, which are more specific for complications of ulcerative colitis. Other options such as Ulcerative Colitis Activity Index and Complete Blood Count are not relevant to the diagnosis of complications. Abdominal X-ray might show pneumatosis coli, but it lacks the ability to visualize mesenteric lymphadenopathy and ascites.

**Clinical Pearls:**

1. Ulcerative colitis can present with complications like intestinal obstruction and pneumatosis coli.
2. Ulcerative colitis can lead to mesenteric lymphadenopathy and ascites, which can be visualized using abdominal ultrasound.
3. Keep in mind that knowledge of these complications is essential for proper diagnosis and treatment of ulcerative colitis patients presenting with abdominal symptoms like those mentioned above.
4. Ultrasound is a non-invasive and safe diagnostic modality that can help in identifying complications of ulcerative colitis.

**Why the Correct Answer is Right:**

Abdominal ultrasound is the correct answer because it can visualize complications such as mesenteric lymphadenopathy and ascites, which are more specific for complications from ulcerative colitis. Ulcerative colitis activity index and complete blood count are not relevant to the diagnosis of complications. Ab