Intestinal absorption and unmediated permeation of sugars in post-infective tropical malabsorption (tropical sprue)

Differential absorption of D-xylose and 3-O-methyl-D-glucose, and unmediated intestinal permeation of lactulose and L-rhamnose has been investigated in 14 patients with diarrhoea following tropical exposure and in 16 healthy control subjects. Five had malabsorption of fat, D-xylose and B12 ('tropical malabsorption' (TM) group), and that was absent or minimal in the others ('tropical diarrhoea' (TD) group). After combined ingestion of the four test sugars in iso-osmolar solution a marked depression in plasma D-xylose concentration (with a slow rise) occurred in all of the TM group; the TD group did not differ significantly from the controls. In contrast, 3-O-methyl-D-glucose absorption was similar in all three groups. Urine analysis demonstrated that intestinal permeation of lactulose was increased and that of rhamnose decreased in the TM group compared with the controls. Ingestion as a hyperosmotic solution further enhanced abnormal lactulose permeation in the TM group. Although some of the TD group showed one or the other of these changes, discrimination of the TM group from the TD and control groups was improved when results were expressed as lactulose/rhamnose differential permeation ratios, especially when using a hyperosmotic stress. Similar abnormalities have previously been demonstrated in untreated gluten-induced enteropathy (coeliac disease). The magnitude of the absorption defects demonstrated in TM are more severe than would be anticipated from the jejunal mucosal abnormalities alone; this suggests that there is probably significant pathology in the distal small intestine (including the ileum) in TM.