A previously healthy 3-year-old Caucasian male presents to the emergency department with fever, left lower extremity pain, and refusal to bear weight. Vitals are as follows:

• Heart rate, 133
• Blood pressure, 100/64
• Respiratory rate, 26
• Oxygen saturation, 97% on room air
• Temperature, 37.5 °C

Physical exam is remarkable for bilateral hips abducted and externally rotated at rest with limited range of motion in his left lower extremity without joint swelling or erythema. Lab results are as follows:

• White blood cell (WBC), 10.49 x 10³/mcL
• Hemoglobin, 10.6 g/dL
• Platelets, 102 x 10³/mcL
• Absolute neutrophil count, 4.83 x 10³/mcL
• Mean cell volume, 75.2 fL
• Sodium, 134 mmol/L
• Potassium, 4.1 mmol/L
• Chloride, 103 mmol/L
• Carbon dioxide, 27 mmol/L
• Calcium, 10.7 mg/dL
• Blood urea nitrogen, 5 mg/dL
• Creatinine, 0.23 mg/dL
• Phosphorus, 4.9 mg/dL
• Magnesium, 1.7 mg/dL
• Total bilirubin, 0.5 mg/dL
• Aspartate aminotransferase, 118 unit/L
• Alanine transaminase, 15 unit/L
• Alkaline phosphatase, 162 unit/L.

Bilateral hip ultrasound is remarkable for trace bilateral hip joint fluid with apparent synovial thickening. He is admitted for orthopedic consultation and started on scheduled ibuprofen due to concern for transient synovitis.

The following day, MRI with and without contrast of bilateral hips is remarkable for pronounced lymphadenopathy involving the right iliac chain and extending to the lower aortocaval junction, possible necrotic lymph node along the right iliac chain, geographic areas of abnormal enhancement involving both iliac bones, focal enhancing lesion in the left acetabulum, and bilateral muscle edema within the iliacus and gluteus minimus muscles. Labs are repeated, and results are as follows:

• White blood cell (WBC), 8.07 x 10³/mcL
• Hemoglobin, 10.3 g/dL
• Platelets, 68 x 10³/mcL
• Absolute blast, 0.23 x 10³/mcL
• Absolute neutrophil count, 4.42 x 10³/mcL
• Lactate dehydrogenase, 2464 unit/L
• Uric acid, 5.4 mg/dL
• Activated prothrombin time, 14.1 seconds
• International normalized ratio, 1.00
• Partial thromboplastin time, 24.5 seconds
• Fibrinogen, 712 mg/dL.

Peripheral blood flow cytometry returns with 2.8% phenotypically abnormal B-lymphoblasts consistent with B-lymphoblastic leukemia/lymphoma.

While awaiting bone marrow aspirate findings, lab results are as follows:

• Sodium, 139 mmol/L
• Potassium, 3.5 mmol/L
• Chloride, 108 mmol/L
• Carbon dioxide, 30 mmol/L
• Calcium, 15.8 mg/dL
• Blood urea nitrogen, 15 mg/dL
• Creatinine, 0.36 mg/dL
• Phosphorus, 5.1 mg/dL
• Ionized calcium, 2.22 mmol/L
• 1,25 vitamin D,
• Parathyroid hormone,
• Parathyroid hormone-related peptide, 1.9 pmol/L (normal 

Based on the clinical presentation and lab results, what is the most likely mechanism of this patient’s hypercalcemia?

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Jillian Fry, MD
Karen Lewing, MD
Children’s Mercy Kansas City
Kansas City, MO, USA

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