Hypophosphatemia and hyperparathyroidism in a case of Bartter's syndrome

In an 18-year-old boy with Bartter's syndrome, hypophosphatemia was discovered (2.4 mg/100 ml) with normal serum calcium concentration (9.7 mg/100 ml) and elevated alkaline phosphatase level: 528 mU/ml (normal less than or equal to 150). Skeleton X-rays showed osteomalacia on the pelvic bones and metaphyseal rickets on the wrists. Plasma 25-hydroxycholecalciferol (25-OHCC) concentration was 7.2 ng/ml (normal = 13 +/- 4.4), and serum immunoreactive parathyroid hormone (iPTH) concentration 160 micron1Eq/ml (normal less than or equal to 150). Ca infusion (1500 mg/m2/12 h) induced an increase in serum P level to 3.2 mg/100 ml, in tubular phosphate reabsorption from 72 to 90%, while serum iPTH decreased to 33 micron1Eq/ml. Vitamin D2 administration (45 mg) resulted in increased 25-OHCC concentration to 28 ng/ml and in healing of pelvic osteomalacia. However, there was little change of the radiological aspect of the wrist and of serum phosphorus and iPTH concentrations. In a control 6-year-old hypokalemic girl, administration of parathyroid hormone (8 USP/kg) produced a marked phosphaturic response and an increase in urinary cyclic AMP excretion. These data suggest that hypophosphatemia can be attributed to secondary hyperparathyroidism in the patient with Bartter's syndrome. Hypokalemia does not impair the renal activity of parathyroid hormone.