Tropical sprue

Definitions & Key takeaways

Tropical sprue is a condition that affects the small intestine and is characterized by malabsorption of nutrients, particularly vitamin B12 and folate. It is thought to be due to bacterial overgrowth, most commonly of Klebsiella, E. coli, and Enterobacter species. Symptoms of tropical sprue may include diarrhea, weight loss, anemia, abdominal pain, bloating, and fatigue. Treatment for tropical sprue typically involves using antibiotics to reduce bacterial overgrowth, and nutrition replacement to deal with specific deficiencies like folate and Vitamin B12.

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Introduction0:00–0:32

Tropical sprue is a gastrointestinal disease that results in malabsorption of nutrients and water. Just like the other “sprue” disease - celiac sprue, 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.

Causes0:32–0:54

The most widely accepted theory is that an acute intestinal infection – bacterial, viral, or protozoal – initially damages the intestinal lining, and causes the first bit of inflammation.
In response, the intestinal cells secrete enteroglucagon, a hormone that decreases intestinal motility. Decreased motility means that food’s allowed to linger in the intestines for longer than usual.

Pathology0:54–2:23

More food means more resources, so this sets the stage for a change in the normal bacterial flora - leading to bacterial overgrowth.
Bacterial overgrowth refers to the idea that some organisms begin to overpopulate and thereby dominate the bacterial ecosystem of the intestines.
In tropical sprue Klebsiella, E. coli, and Enterobacter end up becoming those dominant bacteria.
These dominant bacteria 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 - 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 their surface area dramatically, which means less nutrients and water can be absorbed across the intestinal wall, leading to malabsorption.
This (1) means more food is left behind for the bacteria - leading 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.

Symptoms and complications2:23–2:56

Tropical sprue typically affects adults and the usual pattern is of a chronic disease with exacerbations or flare ups from time to time.
The most common symptoms related to intestinal injury and malabsorption - diarrhea, abdominal pain, fatigue, weight loss, and dehydration.
One complication that can result from malabsorption of vitamins like folate and vitamin B12 is megaloblastic anemia - where the bone marrow produces large, immature red blood cells.

Diagnosis2:56–3:57

The diagnosis of tropical sprue is usually made in individuals who have lived in the tropics and have long-standing gastrointestinal symptoms and malabsorption.
Fat malabsorption can be investigated by doing a 72-hour stool collection test while on a prescribed diet. Carbohydrate malabsorption can be assessed using a D-xylose absorption test.
Normally, if it’s absorbed in the intestines, it gets into the bloodstream and ultimately filtered out into the urine. If it’s not absorbed, less ultimately gets excreted in the urine.
In addition, imaging techniques can also be used to help make the diagnosis. For example, villous atrophy can be seen by endoscopy and a barium swallow may show intestinal wall thickening, which often happens with chronic inflammation.
The ultimate gold standard, however, would be a tissue biopsy of the jejunum to directly visualize the intestinal inflammation and villous atrophy.

Treatment3:57–4:14

Treatment for tropical sprue typically involves using antibiotics to reduce the bacterial overgrowth, and nutrition replacement to deal with specific deficiencies like folate and Vitamin B12.
Sometimes these treatments have to be given for up to a year because of the chronic nature of the problem. So, to recap, tropical sprue is a gastrointestinal disease that’s thought to be the result of bacterial overgrowth - most commonly of Klebsiella, E.

Review4:14–4:54

coli, and Enterobacter species. These bacteria release toxic substances as they ferment in the small intestines, which can lead to chronic inflammation and subsequent flattening of the small intestinal microvilli - ultimately resulting in malabsorption and related abdominal symptoms.
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