Postsplenectomy cytomegalovirus mononucleosis is a distinct clinicopathologic syndrome.

Lymphocytosis in response to viral infection, such as infectious mononucleosis, rarely exceeds 20 x 10(9)/L in the adult population. Transfusion-acquired cytomegalovirus (CMV) mononucleosis after trauma-related splenectomy may cause prominent lymphocytosis, but the history and timing usually hint at the diagnosis. We describe a case of severe CMV mononucleosis that was acquired naturally decades after splenectomy. Together with the 2 similar cases that we reported recently, these cases all presented as initial diagnostic challenge because of a remote history of splenectomy, a prolonged febrile illness (approximately 4 weeks), marked lymphocytosis (peak 27.9 x 10(9)/L), and undetectable or weakened anti-CMV IgM antibody response. The diagnosis was eventually established through detection of circulating CMV antigen or DNA and a year or longer follow-up with serial determination of IgM and IgG antibodies. Two similar cases were also identified in the literature and reviewed. Although the impaired IgM response may confuse the diagnosis, it correlates well with recent studies showing that human blood IgM memory B cells are circulating splenic marginal zone B cells; asplenic or splenectomized individuals, irrespective of the underlying cause, have undetectable IgM memory B cells. Together, these findings suggest that distant or recent postsplenectomy CMV mononucleosis represents a distinct clinicopathologic syndrome resulting from poor control of early viremia because of the lack of both splenic filtration and the typical brisk IgM response. For the practicing clinician, recognizing these features may aid timely diagnosis and treatment.