MON-777 - Low-Dose Zoledronic Acid Successfully Treats Refractory Hypercalcemia in Neonatal Subcutaneous Fat Necrosis

Background
Subcutaneous fat necrosis of the newborn (SFNN) is a rare panniculitis that is associated with perinatal stress. Its most serious complication is severe hypercalcemia and threatens life. Treatment becomes challenging when conventional therapies fail, and evidence regarding optimal treatment strategies is limited.

Case Presentation: We report the case of a newborn delivered by cesarean section at 39 weeks due to fetal suffering, with perinatal asphyxia, macrosomia, meconium-stained amniotic fluid, and respiratory failure that required mechanical ventilation. At 72 hours after birth, indurated erythematous-violaceous plaques appeared on the back, arms, and posterior thighs. Skin biopsy demonstrated lobular panniculitis with necrotic adipocytes, lymphohistiocytic infiltrate, and cholesterol crystal deposition, confirming SFNN. At day 26, progressive hypercalcemia developed, peaking at 16.9 mg/dL. Laboratory tests revealed suppressed parathyroid hormone levels and elevated 1,25-dihydroxyvitamin D. Initial management with parenteral hydration, loop diuretics, and systemic corticosteroids resulted in only transient improvement, followed by recurrent hypercalcemia and development of nephrocalcinosis and pericardial calcifications.
Intervention and Outcome: Given lack of response to first- and second-line therapies, a single low dose of intravenous zoledronic acid (0.0125 mg/kg) was administered. This resulted in rapid and sustained normalization of serum calcium levels without acute adverse effects. Adjunctive therapies were discontinued shortly afterwards. During follow-up, calcium levels persisted normal, renal function was preserved, cutaneous lesions resolved completely and previously identified renal and cardiac calcifications disappeared on imaging.

Conclusion: Low dose zoledronic acid was safe and effective for severe, recurrent hypercalcemia secondary to neonatal subcutaneous fat necrosis. Early recognition and timely use of third-generation bisphosphonates may prevent end-organ complications in affected newborns.

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