Tropical sprue pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Pathophysiology

Pathogenesis

Pathogenesis of tropical sprue is unclear and multiple theories are proposed.The factors involved in the pathogenesis of tropical sprue include:

• Small intestinal bacterial overgrowth affects the enterocyte brush border activity. Bacteria also affect the duodenal morphology causing villous atrophy and increased number of lymphocytes in the intestinal cells.
• Impaired host immune response resulting in prolonged inflammation of the small bowel
• Reduced gut defense mechanisms
• Intestinal villous atrophy
• Bile acid deconjugation affects the enterohepatic circulation and cause steatorrhea.
• Vitamin B12 deficiency causing megaloblastic change in the intestinal mucuosal epithelium
• Slow mouth to ceacum transit due to intestinal stasis promotes small intestinal bacterial over growth. Patients with tropical sprue have higher levels of enteroglucagon, peptide YY, and neurotensin which decrease the motility of intestine.
• Mucosal disaccharidase deficiency : Patients with tropical sprue have higher levels of urinary lactulose excretion suggesting a deficiency of lactase enzyme.
• Post infectious diarrhea: This theory is supported by the occurrence of the disease following an episode of acute gastroenteritis, occurrence of the disease in epidemics in rural areas with poor sanitation, susceptibility of visitors from developed countries to endemic regions and the frequency of small bowel bacterial overgrowth in patients with tropical sprue.

Microscopic Pathology

• Small bowel biospy reveals similar changes as gluten sensitive enteropathy.
• The features demonstrated on a duodenal biopsy include :
  • Villous blunting
  • Intra epithelial lymphocytosis
  • Eosinophilic infilteration of the mucosa