Adult celiac disease and the severe "flat" small bowel biopsy lesion.

Classification of architectural changes in the small intestinal biopsy may be clinically useful to define the cause of diarrhea or suspected malabsorption, especially in adults. Pathologic changes may include severe (flat) or variably severe (mild or moderate) abnormalities. For some disorders, small bowel biopsy findings may be very distinctive and lead to a specific diagnosis. For others, like adult celiac disease, biopsy changes are less specific. Indeed, it is becoming increasingly appreciated that several conditions can produce similar histopathologic changes. Serological assays, including endomysial antibodies and tissue transglutaminase antibodies, may be very useful tools for screening and case finding in clinical practice. However, demonstration of characteristic changes in the small intestinal biopsy is critical, along with a gluten-free diet response.