Pseudohypoparathyroidism: Responsiveness to Parathyroid Extract Induced by Vitamin D2Therapy

Abstract

Response to bovine parathyroid extract (PTE) was tested in an 11 8/12-yr-old girl with pseudohypoparathyroidism before and during treatment with large doses of vitamin D₂. Prior to vitamin D₂ therapy, there was a slight but subnormal calcemic response and no phosphaturic response to large doses of PTE. Response to the same dose of PTE was tested again while the patient was receiving sufficient vitamin D₂ (100,000 IU/day) to restore serum calcium, serum phosphate and the renal handling of phosphate to normal ranges. The serum calcium rose promptly from 10.0 to 14.4 mg/100 ml in response to intramuscular PTE injection and there were marked increases in urinary phosphate excretion rate and phosphate clearance and a decrease in % TRP. The hypercalcemic response to PTE was also demonstrable when the patient received a very low intake of calcium, indicating that bone calcium was mobilized in response to the PTE administration in the vitamin D₂ treated patient. We conclude that large doses of vitamin D₂ improved the responsiveness of our patient with pseudohypoparathyroidism to PTE, an effect not hitherto reported. The findings indicate that the parathyroid hormone response test may be unreliable as a means of diagnosing pseudohypoparathyroidism if the patient is already receiving vitamin D₂ therapy.