Severe gastritis secondary to Epstein-Barr viral infection. Unusual presentation of infectious mononucleosis and associated diffuse lymphoid hyperplasia in gastric mucosa.

Infectious mononucleosis is usually a self-limited clinical syndrome caused by primary Epstein-Barr virus infection. It is occasionally compounded by severe complications involving many different organ systems. Predominant gastrointestinal involvement is rarely documented. We present an unusual case of acute Epstein-Barr virus infection-associated gastritis with diffuse atypical lymphoid hyperplasia in gastric mucosa. The clinical, radiographic, histopathologic, immunohistochemical, and in situ hybridization features needed for accurate diagnosis and differentiation from gastric malignancies are discussed.