American Board of Internal Medicine (ABIM) Certification Practice Exam

Which of the following examples is associated with osmotic diarrhea?

1. Inflammatory bowel disease

2. Magnesium sulfate laxative use

3. Bile acid malabsorption

4. Diabetes mellitus

The correct answer is: Magnesium sulfate laxative use

Osmotic diarrhea occurs when there is an increased osmotic load in the intestines, which draws water into the bowel lumen and leads to diarrhea. This can happen when certain substances are not absorbed well in the intestines, resulting in excess fluid being retained in the gastrointestinal tract. The use of magnesium sulfate as a laxative exemplifies this type of diarrhea. Magnesium sulfate is an osmotic agent that works by holding water in the intestines, thereby increasing stool liquidity and promoting bowel movements. When administered, it increases the osmotic pressure in the intestines, which can result in diarrhea due to the influx of water. In other contexts, inflammatory bowel disease, bile acid malabsorption, and diabetes mellitus are generally associated with different mechanisms of diarrhea. For example, inflammatory bowel disease often leads to inflammatory changes in the bowel mucosa, which can cause secretory or inflammatory diarrhea rather than osmotic. Bile acid malabsorption typically results in diarrhea due to poorly absorbed bile salts affecting the colonic fluid absorption. Lastly, while diabetes mellitus can lead to various gastrointestinal symptoms, such as diabetic gastroparesis, it is usually characterized by a different pathophysiological mechanism than that seen in osmotic diarrhea. Therefore, magnesium sulfate laxative use