Parvovirus B19-Induced Aplastic Crisis and Hemophagocytic Lymphohistiocytosis in a Child With Hereditary Spherocytosis.

Parvovirus B19 (PVB19) is a common virus that usually causes a mild and self-limiting illness. However, in patients with hereditary spherocytosis (HS), it can lead to severe complications such as aplastic crisis and, rarely, hemophagocytic lymphohistiocytosis (HLH). We report a six-year-old boy with HS who presented with persistent fever and severe anemia. Laboratory tests revealed a progressive pancytopenia, including a sudden drop in hemoglobin from 10 to 6.8 g/dL, hyperferritinemia (5,129 ng/mL), elevated soluble IL-2 receptor (1,179 U/mL), mild hypofibrinogenemia, and positivity for PVB19 IgM. Bone marrow examination revealed hypercellularity with the absence of mature erythroblasts, numerous giant proerythroblasts, and hemophagocytic histiocytes, findings consistent with PVB19-associated aplastic crisis and HLH. The patient was treated with intravenous immunoglobulin and prednisolone, resulting in rapid resolution of fever and hematologic recovery. PVB19-induced HLH is extremely rare, accounting for a small percentage of infection-associated HLH cases in Japan. This case underscores the need for vigilance regarding PVB19 infection in HS patients, as overlapping aplastic crisis and HLH may cause rapid anemia progression and organ dysfunction if not promptly recognized and treated.