False-positive infectious mononucleosis spot test in lymphoma

Two patients were recently evaluated for lymphadenopathy. In the diagnostic work-up, a positive infectious mononucleosis spot test was obtained on each patient indicating the presence of horse red cell agglutinins in the blood. This information was somewhat misleading initially as to the etiology of the lymphadenopathy. Subsequent biopsy demonstrated Hodgkin's disease, nodular sclerosing type, in one patient and malignant lymphoma, poorly differentiated lymphocytic type, in the other patient. The experience with these two patients demonstrates that a false-positive mono spot test may occur in malignant lymphoma. In patients with clinical lymphoreticular disease not typical of infectious mononucleosis, a positive spot test should be viewed with caution, and further evaluation and follow-up carried out. EB virus antibody studies indicated that both patients had past infection with EB virus.