Hypoparathyroidism after I-131 therapy with subsequent return of parathyroid function

A 22-year-old woman developed hypoparathyroidism in 1970, 10 months after treatment of hyperthyroidism with I-131. The hypocalcemia was corrected with Vitamin D2 and oral calcium and she remained normocalcemic for 8 yr. In 1979 hypercalcemia was found and Vitamin D2/calcium was discontinued. Because she remained normocalcemic without therapy for 3 yr, we measured the levels of immunoreactive and bioactive PTH in plasma stored since 1970 and in plasma obtained in 1982 to determine whether there had been restoration of parathyroid function. Indeed, PTH levels in 1970 while the patient was hypocalcemic were low. The bioactive PTH was 0.26 pg/ml (normal 1.5-30), whereas--COOH terminal immunoreactive PTH was 620 pg/ml (normal 600-1500) and midmolecule immunoreactive PTH was 433 pg/ml (normal 300-900). In 1982 while normocalcemic the bioactive PTH and immunoreactive PTH were normal (5.18 pg/ml;--COOH, 970 pg/ml; midmolecule, 789 pg/ml, respectively). Thus, an unusual case of hypoparathyroidism after I-131 therapy with return of parathyroid function is documented by measurements of both immunoreactive and bioactive PTH.