Transient pseudohypoparathyroidism as a cause of late-onset hypocalcemia in neonates and infants.

BACKGROUND/PURPOSE: Transient pseudohypoparathyroidism is a rare cause of late-onset hypocalcemia in neonates and infants. The purpose of this study was to investigate the clinical presentation and natural course of transient pseudohypoparathyroidism in neonates and infants.

METHODS: From 1995 to 2006, 21 patients under 3 months of age were admitted to our department because of late-onset neonatal hypocalcemia. Among these, five were noted to have transient hypocalcemia, hyperphosphatemia and elevated serum parathyroid hormone levels. Their clinical data, biochemical findings and natural course were thoroughly analyzed.

RESULTS: All five patients were boys with increased neuromuscular irritability as their initial clinical manifestation. Initial biochemical data showed calcium 1.5 +/- 0.16 mmol/L, phosphorus 9.6 +/- 1.5 mg/dL, intact parathyroid hormone 182 +/- 93 pg/mL and tubular reabsorption of phosphorus 94.8 +/- 3.7%. Two of the patients had magnesium deficiency. After reduction of phosphorus intake and supplementation with calcium and/or magnesium as indicated, the biochemical derangements resolved in 28 +/- 3 days.

CONCLUSION: Neuromuscular irritability is usually the initial clinical presentation of transient pseudohypoparathyroidism. Aside from delayed renal maturation, pseudohypoparathyroidism is also caused by magnesium deficiency. Such a disturbance usually resolves before 3 months of age.