A previously healthy 2-year-old Caucasian female is seen in the emergency department with complaints of rash, fever, and arm pain. Parents report a several month history of intermittent urticarial rash with new onset fevers and arm pain.

The patient’s vitals are as follows: heart rate 134, blood pressure 94/52, respiratory rate 18, oxygen saturation 98% on room air, temperature 38.4 °F.

The exam reveals bruising on upper and lower extremities with mild urticarial rash on chest and abdomen. The patient has no jaundice. The exam is otherwise unremarkable.

Lab results are as follows: white blood cell (WBC) count 4.74 × 10³/mcL, hemoglobin 7.0 g/dL, platelet count 28 × 10³/mcL, absolute neutrophil count 2.03/mcL, 12% blasts, median cell volume 91 fL. Prothrombin time 14.1 seconds (range 11.3-15.6 seconds), international normalized ratio 1.00, partial thromboplastin time 33.3 seconds (range 24.5-37.5 seconds), and fibrinogen 489 mg/dL. Electrolytes and liver function panel are within normal limits. Uric acid is 1.9 mg/dL and LDH 2992 unit/L (range 370-645 unit/L).

Peripheral blood flow cytometry returns with 20% leukemic cells positive for CD117, CD33 (partial), CD61, CD123 (partial), and RAM phenotype.

Based on the clinical presentation and lab results, what would you expect to see on the peripheral smear?

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Amy Johnson, MD, Fellow; and Karen Lewing, MD, Associate Professor of Pediatrics, Fellowship Program Director
Division of Pediatric Hematology, Oncology, & BMT
Children’s Mercy Kansas City, Kansas City, MO, USA

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