Hypercalcemia of Malignancy in a Case of Peripheral Nerve Sheath Tumor: Elucidating the Roles of Simultaneous Mechanisms

Abstract

Hypercalcemia of malignancy (HCM) is caused by 1 of 5 known mechanisms including systemic release of ectopic parathyroid hormone (PTH)-related protein (PTHrP), calcitriol, PTH, cytokines, or destruction of bone by osteolytic metastases. We report the first case of 2 simultaneous mechanisms for HCM in a patient with a peripheral nerve sheath tumor (PNST). PubMed and Google Scholar searches were performed using "hypercalcemia of malignancy" as the search term. A 26-year-old woman with neurofibromatosis presented with worsening left hip pain. Magnetic resonance imaging showed a large left paraspinal mass, subtotal resection of which confirmed PNST. Despite chemo-radiation therapy, the tumor progressed over 16 months, requiring tumor debulking and L3-4 lumbar laminectomy. The patient developed progressive bilateral lower extremity weakness due to direct tumor invasion of the lumbosacral vertebrae with concurrent hypercalcemia. Ionized calcium was 1.47 mmol/dL (reference range is 0.95 to 1.32 mmol/dL), PTH was <4.0 pg/mL (reference range is 8 to 85 pg/mL), 25-hydroxyvitamin D was 14 ng/mL, calcitriol was <8.0 pg/mL (reference range is 18 to 78 pg/mL), PTHrP was 40 pg/mL(reference range is 14 to 27 pg/mL), urinary calcium was <2.0 mg/24 hours, serum C-telopeptide was 1,008 pg/mL (reference range is 64 to 640 pg/mL), and bone-specific alkaline phosphatase was 15.7 μg/L (reference range is 4.7 to 17.8 μg/L). Her serum magnesium, phosphorus, and creatinine levels were normal. Intravenous zoledronic acid and hydration resulted in a normal ionized calcium. Additional imaging revealed extensive tumor invasion of L3-S1 vertebrae. Due to her poor response to all cancer therapies, the patient was discharged to home hospice services. HCM due to PTHrP and osteolytic metastases has not been independently reported to our knowledge in association with malignant PNST as in our patient. The therapeutic importance of characterizing the mechanism of HCM is further discussed in detail.