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Chronic Diarrhea 1

Chronic diarrhea
physiology

Question

Vignette:

A 25-year-old male is admitted to the hospital for an evaluation of chronic diarrhea. His symptoms started about one year ago and have gradually worsened over time. The patient reports that he has 4-5 loose stools per day but denies any blood or mucus in the stool. He also denies any abdominal pain, nausea, vomiting, or weight loss. His medical history is unremarkable. His physical examination is normal except for mild dehydration. His serum sodium level is 137 mEq/L, potassium level is 4.2 mEq/L, and bicarbonate level is 22 mEq/L. Stool studies show an osmotic gap of 100 mOsm/kg.

Question:

What is the most likely cause of the patient’s chronic diarrhea?

Choices

A) Excess bile acids in the colon

B) Inadequate digestion of dietary fats

C) Osmotically active solutes in the lumen

D) Secretory neoplasm of the intestinal mucosa

E) Uncontrolled parasympathetic stimulation

Answer

C) Osmotically active solutes in the lumen

Explanation

The patient's chronic diarrhea and the presence of a high osmotic gap in the stool studies suggest that the diarrhea is osmotic in nature. Osmotic diarrhea occurs when osmotically active solutes (i.e., poorly absorbed substances such as lactose, sorbitol, magnesium, and phosphate) accumulate in the intestinal lumen and draw water into the lumen, leading to loose stools. This is in contrast to secretory diarrhea, which is caused by an increase in active secretion or an inhibition of absorption. Secretory diarrhea continues even with fasting, whereas osmotic diarrhea stops with fasting. The causes of osmotic diarrhea can be dietary, medication-related or due to malabsorptive disorders. In this patient, the absence of abdominal pain, weight loss, and other systemic symptoms makes a secretory neoplasm less likely. Additionally, excess bile acids or inadequate digestion of dietary fats would likely result in steatorrhea, which is not reported in this patient. Uncontrolled parasympathetic stimulation usually presents with other symptoms such as salivation, lacrimation, urination, and defecation.

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