Extreme hyperleukocytosis and blueberry muffin skin lesions as the initial presentation of neonatal leukemia: a case report

BACKGROUND: Neonatal leukemia is a rare and aggressive hematologic malignancy, accounting for less than 1% of pediatric leukemias. Mixed phenotype acute leukemia (MPAL) is particularly uncommon in this age group and poses significant diagnostic and therapeutic challenges. Hyperleukocytosis and leukostasis are life-threatening complications requiring urgent intervention. CASE PRESENTATION: We report the case of a 7-day-old male neonate, small for gestational age, who presented with extreme hyperleukocytosis (peak leukocyte count: 615,400/µL), severe anemia, thrombocytopenia, and generalized purpuric skin lesions consistent with blueberry muffin syndrome. The clinical course was complicated by coagulopathy and a high risk of tumor lysis syndrome. Cytoreductive management included manual partial exchange transfusion due to the unavailability of leukapheresis, achieving transient leukoreduction. Flow cytometry identified two abnormal populations: B-lineage blasts expressing CD19, CD79a, and cytoplasmic CD22, and a myeloid/monocytic population expressing myeloperoxidase (MPO), CD13, and CD33. Lineage assignment was established according to World Health Organization (WHO, 5th edition) and International Consensus Classification (ICC) lineage-defining criteria, confirming MPAL, B/myeloid subtype. Cytogenetic analysis revealed a karyotype 46,XY, add(19)(p13), while molecular testing for KMT2A rearrangements and other recurrent fusion genes was negative. Induction chemotherapy was initiated after initial stabilization; however, the patient died 45 days after diagnosis due to disease progression. CONCLUSION: This case highlights the diagnostic complexity and aggressive clinical course of neonatal MPAL, particularly in the absence of KMT2A rearrangements, and emphasizes the biological heterogeneity of this entity. Strict application of WHO/ICC lineage-defining criteria is essential to ensure accurate classification. Exchange transfusion may serve as a feasible bridging cytoreductive strategy in neonates with life-threatening hyperleukocytosis when leukapheresis is not available, although its effects are temporary and do not replace definitive therapy. Early recognition, prompt supportive management, and improved molecular characterization are critical to optimizing outcomes in this rare and high-risk population.