Bone Abstracts

Background: Idiopathic infantile hypercalcemia (IIH) is a rare disorder caused by CYP24A1 loss-of-function mutation, resulting in impaired degradation of 1,25-dihydroxyvitamin D₃. Typical signs include muscle hypotonia, dehydration, failure to thrive, psychomotor retardation, constipation, nephrocalcinosis. IIH should be distinguished from other causes of hypercalcemia in infancy. Treatment includes low calcium diet, glucocorticoids, furosemide, calcitonin. Pamidronate, an intravenous bisphosphonate, which is a potent inhibitor of bone resorption, has been so far used only in infants with osteogenesis imperfecta, hypercalcemia due to Williams–Beuren syndrome or neonatal severe primary hyperparathyroidism, and just once in IIH.

Case report: We present a case of previously healthy 5-month old boy with IIH, where calcemia peaked to 5 mmol/l. The boy suffered from poor apetite, dehydration, constipation, and failure to thrive. Treatment with methylprednisone and furosemide had only minor effect, therefore two intravenous infusions of pamidronate (0.6 mg/kg per dose) were necessary to correct the serum calcium level to 2.95 mmol/l. Furthermore, CYP24A1 homozygous mutation p.R396W (c.1186c>t) was identified in this patient, confirming the clinical diagnosis of IIH. Currently, the boy is 5 years old, thriving with normal psychomotor status and is being followed on an out-patient basis.

Conclusion: IIH has a favourable outcome once properly detected and appropriately treated. Pamidronate has a beneficial effect in those patients with IIH where glucocorticoids and furosemide fail to meet the expectations.