#00066751

An 11-month-old boy with Crigler-Najjar syndrome (UGT1A1 mutation), managed with phenobarbital and phototherapy, presented after outpatient labs showed hyperleukocytosis and thrombocytopenia. He was afebrile and hemodynamically stable, with petechiae, mild hematomas, and marked hepatosplenomegaly (5-6 cm below the costal margin). He had no respiratory distress or dehydration. Hb 11 g/dL, WBC 11 × 10³/µL with 96% lymphocytes, platelets 18 × 10³/µL, uric acid 10 mg/dL, total bilirubin 22 mg/dL (indirect 21, consistent with Crigler-Najjar), ALT 190 U/L, AST 126 U/L. G6PD was normal. CSF cytospin (panel A) preparations demonstrating numerous leukemic blasts, characterized by intermediate to large cells with high nuclear-to-cytoplasmic ratio, fine chromatin, and occasional nucleoli (Wright–Giemsa stain; A scale bar 50 and 25 µm).