Pancytopenia Misattributed to Parvovirus B19 Infection Revealing Acute Promyelocytic Leukemia.

Pancytopenia is a diagnostic challenge due to its broad differential diagnosis, including infections and hematological malignancies. Parvovirus B19 infection is a recognized but uncommon cause of transient pancytopenia. However, positive viral serology or viremia may lead to diagnostic anchoring and delay the identification of underlying malignant disorders. We report the case of a 17-year-old previously healthy female presenting with persistent fever and tonsillitis. Laboratory investigations revealed pancytopenia with agranulocytosis. Blood serology and polymerase chain reaction (PCR) were positive for Parvovirus B19. The peripheral blood smear was normal. An initial diagnosis of virus-related pancytopenia was established. Despite supportive treatment, including granulocyte colony-stimulating factor, transfusions, and intravenous immunoglobulins, pancytopenia persisted. Bone marrow aspiration and biopsy were performed. The bone marrow aspiration showed a hypercellular marrow without abnormal cells by flow cytometry within the conventional blast gate. Subsequent pathological examination of the biopsy revealed massive blast infiltration consistent with acute promyelocytic leukemia. The patient rapidly developed disseminated intravascular coagulation, and atypical promyelocytes later appeared in the peripheral blood smear. Targeted treatment with all-trans retinoic acid and arsenic trioxide was initiated, leading to remission. This case highlights the risk of delayed diagnosis when pancytopenia is attributed to viral infection. Persistent cytopenia, even in the presence of positive Parvovirus B19 testing and a normal blood smear, should prompt early bone marrow examination to exclude underlying hematological malignancy.