8120 Effective Management of Neonatal Hypercalcemia in Congenital Mesoblastic Nephroma: A Case Report on the Use of Calcitonin

Abstract Disclosure: C.S. Galvez: None. K. Rifai: None. C. Moorthy: None. S. Chheda: None. M. Zerah: None. Introduction: Pediatric patients with hypercalcemia of malignancy are typically treated with hyperhydration, loop diuretics and bisphosphonates. Calcitonin, a peptide functionally antagonizes the effects of PTH. Calcitonin has limited pharmacokinetic data in neonates, especially those with Congenital Mesoblastic Nephroma (CMN), making treatment challenging with unclear safety and efficacy parameters. We present the fourth published case describing the use of calcitonin for likely PTH-rP-mediated severe hypercalcemia in a neonate with CMN. Clinical Case: A 15-day-old late preterm male, presented with lethargy, poor feeds, severe failure to thrive and a large abdominal mass. The mother is a G4P4, with good prenatal care. On admission, the patient was hypertensive (138/84 mmHg) and appeared dehydrated. Physical examination revealed a firm mass in the right abdomen crossing the midline. Serum calcium levels were 13.5 mg/dL (normal 9.0-10.9 mg/dL), with an ionized calcium 1.71 mmol/L (normal 1.15 and 1.30 mmol/L). Abdominal ultrasound showed a large, 9.1 x 8 cm dominant solid right renal mass, most likely CMN, with left-sided medullary nephrocalcinosis. Cardiac Echo and EKG were within normal limits. The patient received hydration, nicardipine (titrated to decrease blood pressure by 10-15 mmHg per day) and furosemide at 1 mg/kg/day IV q6h. Due to the persistence of hypercalcemia after 24 hours of treatment (14.7 mg/dL serum calcium with ionize of 1.81 mmol/L), the patient received one dose of calcitonin (4 units/kg subcutaneously), resulting in a decrease in serum calcium to 11.5 mg/dL in 4 hours. The patient underwent a successful radical right uretero-nephrectomy, with post-surgery improvement of neurological, cardiovascular and electrolyte status. Unfortunately, PTH-rP sample was insufficient. Pathology reported CMN of the cellular type. CMN is a rare tumor with low malignant potential, representing approximately 3% of all pediatric renal tumors. It is the most common renal neoplasm diagnosed in the first 6 months of life. The most common symptom is an abdominal mass (76%), with hypertension (19%). Hypercalcemia was reported in only 4% which can be secondary to paraneoplastic secretion of PTH or PTH-rP. Conclusion: This case represents the fourth instance of calcitonin use in a neonate with CMN to manage persistent hypercalcemia. Subcutaneous administration of calcitonin at 4 units/kg proved effective with a short onset of action (within 2 hours) and duration of 6 to 8 hours, making it a viable alternative to bisphosphonates (action around 48 hours and duration of 7 to 14 days). Calcitonin's advantages include less significant side effects and a faster resolution of complications like "Hungry bone Syndrome." The flexibility of repeated dosing every 6 hours, with the option to increase the dose, if necessary, adds to its clinical utility. Presentation: 6/3/2024