Question 228

Question:

A 21-year-old man has weight loss and severe intermittent bloody diarrhea. A barium enema and colonoscopy show multiple ulcers and inflammatory changes extending from the rectum to the mid-transverse colon. Biopsy specimens taken from multiple sites show acute and chronic inflammation restricted to the mucosa. Which of the following is the most likely diagnosis?

Correct Answer: E.  Ulcerative colitis

The key to answering this question is focussing on 4 key points:
1. diarrhea with or without blood
2. location: inflammatory changes are seen in the DISTAL part of the colon only
3. number of lesions: there are multiple ulcerations
4. depth of lesion: these ulcerations are limited to the mucosa.
Ulcerative colitis matches the characterization in the question stem along these 4 four points.
The various diseases listed in the answer choices can best be differentiated based on the 4 points listed above.
In particular, you must be familiar with the differences between Crohn’s disease (B) and Ulcerative Colitis (E).
(A) AIDS associated gastroenteritis results in pathological changes more proximally than described here, and would not selectively target the colon. Futher, AIDS complications rarely result in inflammatory changes.
(B) Crohn’s disease may occur anywhere throughout the colon and occurs in a patchy, discontinuous fashion. It penetrates deeper into the mucosa producing transmural fistulae and inflammation, unlike UC.
(C) C.difficile colitis (also called pseudomembranous colitis) typically affects older patients who have had prior exposure to antibiotics and rarely produces bloody diarrhea.
(D) E. coli is the most common cause of bacterial colitis, and depending on the pathogenic strain, may present differently. Notably, the lamina propria of the large intestine is infiltrated by polymorphonuclear leukocytes, without producing such a pattern of mucosal inflammation.