Diagnosis of atypical cases of infectious mononucleosis

The variable manifestations of infectious mononucleosis rarely cause clinic ians to suspect primary Epstein-Barr virus or cytomegalovirus infection; co nsequently, costly diagnostic tests and unnecessary treatments are undertak en. Seventeen cases of clinically atypical and 11 cases of clinically typic al infectious mononucleosis were diagnosed through screening for atypical a nd apoptotic lymphocytes in the peripheral blood samples by means of an aut omated hematologic analyzer. Atypical and typical cases did not differ sign ificantly with respect to peripheral white blood cell counts; percentages o f lymphocytes, atypical lymphocytes, CD4(+) lymphocytes, human leukocyte an tigen-DR positivity in CD3 lymphocytes, or apoptotic cells in blood smear a fter incubation; or levels of aspartate aminotransferase, alanine aminotran sferase, and lactate dehydrogenase. Only the percentage of CD8(+) lymphocyt es was significantly higher in patients with typical infectious mononucleos is than it was in patients with atypical infectious mononucleosis. Because certain atypical cases of infectious mononucleosis display laboratory abnor malities that are characteristic of typical infectious mononucleosis, enhan ced awareness can help in the diagnosis.