Pathology of equine granulomatous enteritis.

A morphological study on equine granulomatous enteritis (EGE) in 13 horses is presented. All horses were young (1 to 5 years old) standardbreds. Based on gross pathology, cases were classified into those with diffuse (11 cases) and those with localized (2 cases) small bowel lesions. The granulomatous reaction in the gut was marked by diffuse and patchy infiltrates and distinct granulomas, composed of epithelioid cells, macrophages and lymphoid cells, and was devoid of necrosis. Salient accompanying features of the small bowel included lymphoid hyperplasia, peri-lymphatic and transmural inflammation, lymphangiectasia, villous atrophy, mucosal ulcerations and crypt abscesses. Granulomatous changes were often demonstrated in alimentary tract tissues beyond the small bowel and its lymph nodes and were in some cases shown to occur multi-systemically. The morphology and epidemiological features of the condition suggest a specific aetiology. The histology indicated that an immune reaction was operative and that inflammation of the lamina propria was an early event in the pathogenesis of the gut lesion. No conclusive evidence of a specific infectious cause was found. It is suggested that the disease might be associated with intrinsic disturbances of inflammatory defence mechanisms.