Review Question - QID 106673

This patient is presenting with infectious mononucleosis, which is characterized by atypical lymphocytes on microscopic examination.

Infectious mononucleosis (IM) is cause by the Epstein-Barr virus (EBV). IM is usually characterized by fever, pharyngitis (often with exudates), lymphadenopathy (especially posterior cervical nodes), and sometimes hepatosplenomegaly. EBV is transmitted via respiratory secretions. The peak incidence of IM is 15-20 years of age.

Ebell discusses the diagnosis of IM. Following spread of the infection, there is an incubation period of 4-8 weeks. During an acute infection, antibodies are produced, which often have the property that they agglutinate sheep erythrocytes. This fact is used as the basis of the monospot test, which can aid in the diagnosis of EBV IM.

Balfour et al. discuss the atypical lymphocytes (also known as Downey cells) that can be seen in EBV IM. Atypical lymphocytes are activated CD8+ T cells. During acute infection, CD8+ T cells proliferate rapidly. These cells are appropriately responding to EBV infected cells and are vital to the process of EBV elimination. In patients who are unable to mount an appropriate CD8+ T cell response, fulminant EBV infection may occur.

Figure A depicts an atypical lymphocyte seen in EBV. Note the "hugging" of RBCs. Figure B depicts Reed-Sternberg cells seen in Hodgkin's disease. Note the large "owl-eye" nucleoli. Figure C depicts normal lymphocytes. Figure D depicts "smudge cells", which can be seen in B-cell chronic lymphocytic leukemia. Note the characteristic "smudged" appearance. Figure E depicts "hairy" cells that are seen in hairy cell leukemia. Finally, for comparison, illustration A directly compares atypical to normal lymphocytes. Note the appearance and size of the nucleus in each case and the "hugging" of the RBCs by the atypical lymphocytes.

Incorrect Answers:
Answers 2-5: See the description of the Figures above.