Non-steroidal Anti-inflammatory Drug-Induced Severe Eosinophilia and Hematogone Hyperplasia Masquerading as Leukemia: Diagnostic Complexity in a Young Child.

Eosinophilia in pediatric patients may arise from a wide spectrum of underlying etiologies encompassing reactive, clonal, and idiopathic disorders. While reactive eosinophilia is common in childhood and typically related to infections, allergic or atopic disease, hypersensitivity reactions, or systemic inflammatory disorders, clonal eosinophilia is uncommon and may be associated with primary hematological malignancies. The distinction between reactive and clonal eosinophilia is clinically crucial, particularly in the presence of alarming features such as extreme leukocytosis, organomegaly, cytopenias, or circulating blasts that may mimic acute leukemia. We present the case of a three-year-old boy with severe eosinophilia and anemia following a short febrile illness and exposure to a non-steroidal anti-inflammatory drug combination, raising an initial suspicion of leukemia. Bone marrow examination and flow cytometry revealed significant hematogone hyperplasia with no evidence of acute leukemia, supporting a diagnosis of drug-induced reactive eosinophilia. The coexistence of hematogone hyperplasia and eosinophilia in this clinical setting has not been previously described. This case emphasizes the importance of systematic evaluation to avoid misdiagnosis and unnecessary evaluation and treatment.