A 55-YEAR-OLD PHYSICIAN WITH LYMPHOCYTOSIS, FEVER, ABDOMINAL PAIN, AND PROFOUND THROMBOCYTOPENIA. A. Almahameed 1 , A. Absi 2 , D. Farray-berges 2 , S. Rehm 3 ; 1 Cleveland Clinic Foundation, Shaker Heights, Ohio; 2 The Cleveland Clinic Foundation, shaker hts, Ohio; 3 The Cleveland Clinic Foundation, Cleveland, Ohio LEARNING OBJECTIVES: 1-Recognize infectious mononucleosis as a rare cause of severe thrombocytopenia. 2-Utilize EBV-specific antigens to diagnose infectious mononucleosis in monospot-negative patients. 3-Treat EBV-induced severe thrombocytopenia. CASE INFORMATION: A previously healthy 55-year-old male physician reported 2 weeks of fatigue, malaise, and mild abdominal discomfort. On initial evaluation, a right submandibular lymph node was moderately enlarged and the CBC was normal. Several days later, he became febrile (39 C). He had a normal WBC count with lymphocytosis (50%) and atypical lymphocytes (25%), as well as transaminitis (ALT 239 U/L and AST 198 U/L). Monospot tests, CMV titers, HIV antibodies, and blood and urine cultures were all negative. Self-prescribed oral therapy with empiric clarithromycin and ciprofloxacin produced little improvement. One week later, his platelet count was 90,000/mm 3 . He was admitted three days later with petechial rash involving the upper extremities and the upper part of his trunk, and a platelet count of 8,000/ mm 3 . He was afebrile, had diffuse non-palpable, non-blanching petechiae on his upper extremities, ecchymoses on his buccal mucosa, 3 mildly enlarged non-tender lymph nodes in the right submandibular area, and a palpable spleen tip. The WBC count was 10,000/mm 3 with 26% polymorphs and 63% lymphocytes, of which 20% were atypical. His hemoglobin was 13.4 g/dl, and his platelet count was less than 1,000/mm 3 . Blood chemistries and coagulation parameters were normal. Occasional atypical, large lymphocytes and rare platelets were evident on a peripheral blood smear. Bone marrow biopsy showed normocellular composition with severe thrombocytopenia and adequate numbers of megakaryocytes. Flow cytometry of the blood found no malignant cells. Serologies were negative for toxoplasmosis, hepatitis C, hepatitis B, herpes simplex, and herpes virus 6, but the patient had elevated levels of IgM and IgG antibodies to Epstein-Barr virus viral capsid antigen (VCA) (IgG VCA: 152 IU/ml, normal < 18, and IgM VCA 71 TV (normal < 18). The patient was treated with high-dose prednisone and IVIG 1 g/kg/day for 2 days, and his platelet count rose gradually (11,000/mm 3 on discharge and 180,000 mm 3 3 weeks later). DISCUSSION: Infectious mononucleosis (IM) should be included in the differential diagnosis of severe thrombocytopenia in adults even when the initial monospot test is negative. Lowgrade neutropenia and thrombocytopenia are common during the first month of illness. Heterophile antibodies are useful in diagnosing disease in many cases but are often not detectable in children under age 5, in the elderly, and in patients presenting with symptoms not typical of IM. An alternative is EBV-specific antibody testing. Titers of IgM and IgG antibodies to viral capsid antigen are elevated in the serum of more than 90% of patients at the onset of disease. IgM antibody to VCA is useful for the diagnosis of acute IM because levels are elevated only during the first 2 months of the disease. We can not entirely exclude the possibility that ciprofloxacin or clarithromycin therapy caused the thrombocytopenia. Given the clinical illness, the results of serologic testing, and the rarity of profound antibioticassociated thrombocytopenia, we believe that acute Epstein Barr virus infection is the more likely cause of the abnormalities. DISCUSSION: Vitamin B12 comes from the diet and is present in all food products of animal origin. Liver stores of B12 can last for several years after dietary ingestion ceases. Although dietary B12 deficiency is extremely rare, it can occur in vegans who abstain from all such foods for prolonged periods of time.