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Tropical sprue

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Gastrointestinal system

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Tropical sprue

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Tropical sprue

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A 28-year-old man comes to the physician complaining of diarrhea for the last several weeks. He describes his stool as bulky, greasy, and “tends to float on top of the water in the toilet.” The patient has not had similar symptoms in the past. He also unintentionally lost 11-lb over the past month. He is an avid hiker and most recently went on a hike in the Appalachians, where he regularly cooked his own meat and drank water from nearby fresh-water springs. The patient has not had fever, rashes, or any bloody stools. Vital signs are within normal limits. Physical examination shows a mildly tender abdomen with hyperactive bowel sounds. There are patches of skin with hyperkeratosis as well as several bruises. Stool samples are taken and stain positively with Sudan III. If this patient goes untreated, which of the following complications is he most likely to develop?  

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Content Reviewers:

Rishi Desai, MD, MPH

Contributors:

Tropical sprue is a gastrointestinal disease that results in malabsorption of nutrients and water.

Just like the other “sprue” diseases, like celiac sprue which is more often known as celiac disease, in tropical sprue the villi of the small intestine become flattened, but the exact cause isn’t known.

The biggest clue is that tropical sprue seems to mostly affect individuals living in the the tropical regions of the world, like the Caribbean, India, and Southeast Asia.

The most widely accepted theory is that an acute intestinal infection, which could be bacterial, viral, or protozoal, initially damages the intestinal lining, and this causes the first bit of inflammation.

In response, the intestinal cells secrete enteroglucagon, which is a hormone that decreases intestinal motility.

Decreased motility means that food’s allowed to linger in the intestines for longer than usual.

More food means more resources, so this sets the stage for a change in the normal bacterial flora, which leads to bacterial overgrowth.

Bacterial overgrowth refers to the idea that some organisms begin to overpopulate and therefore dominate the bacterial ecosystem of the intestines.

In tropical sprue, Klebsiella, E. coli, and Enterobacter end up becoming those dominant bacteria. These guys release toxic byproducts as they ferment the food that lingers in the gut, and these toxins can damage the intestinal lining, leading to more inflammation.

Over time, all of this chronic inflammation leads to villous atrophy, which is flattening of the villi that line the small intestine.

Villi are important because they provide the surface area and digestive enzymes necessary for nutrient absorption.

Flattening of the villi reduces this surface area, which means less nutrients and water can be absorbed across the intestinal wall, which leads to malabsorption.

This (1) means more food is left behind for the bacteria, which leads to more intestinal wall injury and inflammation, and (2) the malabsorption also causes depletion of vitamin B12 and folate over time.

Unfortunately, folate is needed to help maintain the integrity of the intestinal mucosa, so as levels fall it also further contributes to the intestinal wall injury and inflammation.

Tropical sprue typically affects adults and the usual pattern is of a chronic disease with exacerbations or flare ups from time to time.

Summary
Tropical sprue is a malabsorption disease commonly found in the tropical regions, marked with abnormal flattening of the villi and inflammation of the lining of the small intestine. It differs significantly from coeliac sprue. It appears to be a more severe form of environmental enteropathy.
Sources
  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Tropical malabsorption" Postgraduate Medical Journal (2006)
  6. "AETIOLOGY AND PATHOGENESIS OF POSTINFECTIVE TROPICAL MALABSORPTION (TROPICAL SPRUE)" The Lancet (1984)