Histopathological and immunohistochemical evaluation of 53 cases of feline lymphoplasmacytic enteritis and low-grade alimentary lymphoma.

Low-grade alimentary lymphoma (LGAL) is a recently described entity displaying many microscopical features similar to lymphoplasmacytic enteritis (LPE). The aim of this study was to review the histopathological and immunohistochemical features of LPE and LGAL to determine if specific features are useful in distinguishing between these disorders. Fifty-three cases of LPE (n=24) or LGAL (n=29) were recruited retrospectively and prospectively. Of the 24 cases of LPE, 12 were mild, seven were moderate and five were marked in severity. The ileum and jejunum were the most common sites affected for both LGAL and LPE (70-90% of cases). Involvement of the stomach was more common with LPE (29%) than LGAL (7%) (P<0.0001). Twelve cases of LGAL (41%) had evidence of concurrent LPE. Microscopical features significantly associated with LGAL were epitheliotropism, involvement of the muscularis propria and/or serosa, more severe infiltration and more severe changes to the villus and crypt architecture. Plasma cell infiltration within the mucosa, conversely, was a feature of LPE. Twenty-eight of the 29 cases of LGAL were of T-cell phenotype. While many LGAL and most LPE cases had a mixed infiltrate of T and B lymphocytes, LGAL cases had a clear predominance of the T-cell phenotype. Expression of class II molecules of the major histocompatibility complex by enterocytes did not differentiate between LGAL and LPE. In eight of 12 cases of moderate-marked LPE there was disparity in diagnosis by two pathologists regarding differentiation from LGAL, requiring assessment by a third pathologist to reach a consensus diagnosis. This demonstrates the inherent difficulty in differentiating LPE from LGAL on the basis of microscopical and immunohistochemical features alone. Other diagnostic tools such as clonality testing may assist in the definitive diagnosis of such cases.