A neonate with recurrent tetany: questions

A 14-day-old male neonate was admitted with recurrent tetany for 1 week. He was born after an uncomplicated pregnancy at term with a birth weight of 3080 g. The maternal and family histories were unremarkable. He was fed with standard formula and no other supplements. Starting at age 7 days, he began to develop intermittent focal twitching of all four limbs lasting for 5 to 10 s. His pulse rate was 172 bpm, blood pressure 71/48 mmHg, respiratory rate 66 /min, and body temperature 36.8 °C. Physical examination showed an alert conscious infant without dysmorphic features, heart murmurs, or neurologic abnormalities. Laboratory studies were notable for profound hypocalcemia [total calcium (Ca) 5.0 mg/dl] and hyperphosphatemia [inorganic phosphate (iP) 10.2 mg/dl] with low urinary Ca and iP excretion (UCa/creatinine 0.06 mg/mg, fraction excretion of iP 3.5 %). The remainder of the blood tests showed white blood cells of 13,000/mm with 46 % lymphocytes, Na 136 mmol/l, K 5.6 mmol/l, Cl 105 mmol/l, HCO3 − 22 mmol/l, BUN 5 mg/dl, creatinine 0.3 mg/dl, glucose 75 mg/dl, Mg 1. 6 mg/dl, albumin 3.9 gm/dl, lactate 10 mg/dl, and C-reactive protein 0.5 mg/l. Hormone profiles revealed 25(OH) Vit D3 5 ng/ml (NR: 5–55), 1,25(OH)2 Vit D3 57 ng/ml (NR: 15–55), intact PTH 28 pg/ml (NR: 7–53), free T4 1.53 ng/dl (NR: 0.85–1.58), and cortisol 12.2 μg/dl (NR: 4.2–38.4). Chest X-ray and renal ultrasonography were normal. His convulsions were controlled with intravenous calcium gluconate infusion (400 mg/kg/day) followed by oral calcium carbonate supplementation (50 mg/kg/day) for 6 weeks.