Tabanelli et al. Journal of Medical Case Reports 2011, 5:218 http://www.jmedicalcasereports.com/content/5/1/218 where memory B cells are the physiological reservoir of latent EBV [1]. Nonetheless, rare EBV-driven T cell tumors have been recognized. In this regard, fulminant mononucleosis has recently been demonstrated to be a monoclonal CD8+ LPD, and is cur- rently classified as systemic EBV+ T cell LPD of childhood in the World Health Organization classification of tumors of hematopoietic and lymphoid tissues [5]. This entity is a rare clonal proliferation of EBV-infected T cells with an activated cytotoxic phenotype [5]; the disease occurs with increased frequency in immunocompetent children and young adults, appears to be more common in Asians and Native Americans, and is associated with rapid progression, high morbidity and mortality. It can develop after primary EBV infection or in association with chronic active EBV infection (CAEBV). Despite the name, the disease occurs not only in children but in adolescent and young adults as well, the median age being around 20 years [5]. At morphology, neoplastic T cells are usually small and lack significant cytological atypia [6]. However, cases with pleomorphic medium-sized to large-sized lymphoid cells, irregular nuclei and frequent mitoses have been described. The most typical phenotype is CD2+, CD3+, CD8+, CD56-, and TIA+ [6-8]; conversely, cases arising in the setting of severe CAEBV are CD4+. Neoplastic cells have monoclonally rearranged T cell receptor (TCR) genes, and consistent Epstein-Barr encoded RNA (EBER) positivity at in situ hybridization (ISH). Differential diag- nosis mainly concerns reactive conditions as well as aggressive natural killer (NK) cell leukemia. Here, we report the clinicopathological features of ful- minant T-LPD that arose in the setting of acute primary EBV infection in our patient, characterized by a mono- clonal proliferation of EBV-infected T cells. Case presentation A 23-year-old Caucasian man was hospitalized for per- sisting fever resistant to conventional therapies. On phy- sical examination, our patient presented with marked hepatosplenomegaly and abnormal sounds at thoracic auscultation. Laboratory findings consisted of severe pancytopenia (hemoglobin 9.3 g/dL, platelets 93 × 109 cells/L, white blood cells 2.2 × 109 cells/L, neutrophils 410 × 109 cells/L, lymphocytes 1.570 × 109 cells/L), increased LDH, signs of disseminated intra-vascular coa- gulopathy (CID), and anti-EBV IgM positivity, while a chest X-ray showed diffuse pulmonary infiltrates. No prior immunological abnormalities were recorded. For the suspicion of either massive bone marrow infil- tration by leukemia/lymphoma or hemophagocytic syn- drome a bone marrow biopsy was performed. Results from the biopsy showed the bone marrow was hypercel- lular, with numerous atypical lymphoid cells and occa- sional hemophagocytes (identified by positive staining Page 2 of 5 for CD68/PGM1) (Figure 1). Lymphocytes were more often small and without significant atypia; a smaller per- centage was represented by larger cells (Figures 1 and 2). Immunohistochemistry (IHC) investigation results showed atypical lymphocytes were CD79a-, CD3+, CD2+, CD8+ and TIA1+ (Figure 2). ISH for EBER demonstrated that the majority of lymphoid cells were positive (Figure 2). Finally, polymerase chain reaction (PCR) analysis revealed a monoclonal rearrangement of the TCRg genes. IHC, ISH and molecular analyses were carried out as previously described [9,10]. Based on the above findings, a final diagnosis of sys- temic EBV+ T cell LPD of childhood was made. Our patient was initially treated with two sequential doses of VP16 with moderate improvement of his clinical and laboratory data. In particular, the fever transiently improved, hepatosplenomegaly was reduced, and coagu- lation parameters were partially corrected; however, severe peripheral blood cytopenia persisted. Soon after, the patient developed a fever recrudescence in associa- tion with pulmonary fungal infection. Figure 1 Pathological findings on lymph node biopsy. Giemsa, Ki67 and CD68 immunostains are shown. Arrows indicate atypical cells (GM) as well as eritrophagocytic syndrome (CD68).