A Rare Cause of Hypercalcemia In Adults: Idiopathic Infantile Hypercalcemia

Idiopathic Infantile Hypercalcemia (IIH) is a rare disorder marked by PTH-independent hypercalcemia, usually diagnosed in infancy, with adult cases being uncommon. This report discusses a 60-year-old male with a 25-year history of type 2 diabetes, recurrent kidney stones, and stage 3a chronic kidney disease. Laboratory findings included hypercalcemia, normal phosphorus and 25-hydroxycholecalciferol levels, and suppressed PTH. Urinary ultrasonography revealed medullary nephrocalcinosis. Comprehensive evaluation ruled out malignancies, granulomatous diseases, and endocrinopathies. Genetic testing identified compound heterozygous mutations in the CYP24A1 gene, confirming IIH type 1. Initial management involved calcium- and vitamin D-restricted diets and sunlight avoidance. When hypercalcemia persisted, fluconazole treatment (50 mg/day) was trialed but proved ineffective. Cinacalcet (60 mg/day) was subsequently introduced, successfully normalizing serum calcium levels. Family genetic screening revealed biallelic mutations in two siblings and heterozygous mutations in two others, though none exhibited hypercalcemia. This case underscores the need for heightened awareness of IIH in adults, advocating for family screening to detect asymptomatic carriers early. The effectiveness of cinacalcet in managing adult IIH highlights its therapeutic potential when lifestyle modifications alone are insufficient, preventing long-term complications from untreated hypercalcemia.