Context: Pseudohypoparathyroidism type 1B (PHP1B) patients have PTH resistance at the renal proximal tubule and develop hypocalcemia and secondary hyperparathyroidism. Hyperparathyroid bone disease also develops in some patients. PHP1B patients are at theoretical risk of developing tertiary hyperparathyroidism.
Setting: Patients were studied in a clinical research center.
Patients: Five female PHP1B patients presented with hypercalcemia and elevated PTH.
Intervention: Patients either underwent parathyroidectomy (n = 4) or received cinacalcet (n = 1).
Main outcome measures: Serum calcium and PTH were serially measured before and after intervention.
Results: Five PHP1B patients developed concomitantly elevated serum calcium and PTH levels (range, 235-864 ng/liter) requiring termination of calcium and vitamin D therapy (time after diagnosis, 21-42 yr; median, 34 yr), consistent with tertiary hyperparathyroidism. Four patients underwent parathyroidectomy with removal of one (n = 2) or two (n = 2) enlarged parathyroid glands. Calcium and vitamin D therapy was reinstituted postoperatively, and at 93-month median follow-up, PTH levels ranged between 56 and 182 (normal, <87) ng/liter. One patient was treated with cinacalcet, resulting in resolution of hypercalcemia.
Conclusions: PHP1B patients are at risk of developing tertiary hyperparathyroidism and/or hyperparathyroid bone disease and should therefore be treated with sufficient doses of calcium and vitamin D to achieve serum calcium and PTH levels within or as close to the normal range as possible. Surgery is the treatment of choice in this setting. Cinacalcet may be a useful alternative in those who do not undergo surgery.