Infectious mononucleosis in lymphoid tissue. Histopathology, in situ hybridization, and differential diagnosis.

The histopathologic features of tissue specimens from 16 patients with acute Epstein-Barr virus-induced infectious mononucleosis, which was confirmed by clinical and serologic methods, are described. The clinical course was usually self-limited (14 patients), but it resulted in the death of two patients, one of whom (patient with renal transplantation) was immunosuppressed. Each lymphoid tissue specimen, including those obtained from the lymph nodes (n = 9), tonsils (n = 5), spleen (n = 1), and appendix (n = 1), showed a nonuniform expansion of nonfollicular areas by a polymorphous population of lymphocytes, including transformed lymphocytes and immunoblasts. In situ hybridization demonstrated Epstein-Barr virus-infected lymphocytes in four of eight tissue specimens that were studied. Other histologic features included Reed-Sternberg-like cells, plasma cells, histiocytes, frequent mitoses, abundance of postcapillary venules, and necrosis. These histologic features should suggest a diagnosis of infectious mononucleosis rather than other processes, either benign or malignant, that can mimic it.