Skeletal responsiveness to parathyroid hormone in pseudohypoparathyroidism

Background: Although there have been some case reports suggesting that bone in patients with pseudohypoparathyroidism (PHP) might respond to parathyro id hormone (PTH), no information is available as to whether serum PTH conce ntration is related to bone metabolic markers or to bone mineral density (B MD) in PHP, Objective: To address these relationships, by comparing intact serum PTH, b one metabolic markers and BMD in patients with PHP with those in patients w ith idiopathic hypoparathyroidism (IHP) and postoperative hypoparathyroidis m (OHP), Methods: Intact serum PTH, bone metabolic markers (osteocalcin, tartrate-re sistant acid phosphatase, pyridinoline, deoxypyridinoline) and BMD by dual- energy X-ray absorptiometry or single-photon absorptiometry were measured i n patients with PHP Ia (n = 2) and PHP Ib (n = 8). The results were compare d with those in patients with IHP (n = 5) and OHP (n = 14). Results: All bone metabolic markers measured were present in significantly greater amounts in patients with PHP Ib than in those with IHP+OHP. The Z s core (standard deviation of average BMD at each age) of the BMD of femoral neck was significantly lower in patients with PHP Ib than in those with IHP +OHP, The Z scores of BMD of lumbar spine and radius were also lower in pat ients with PHP Ib than in those with IHP+OHP, but the difference was not si gnificant. Moreover, the intact serum PTH concentrations were significantly and positively related to bone metabolic marker levels in all patients, an d the intact serum PTH concentrations were significantly and negatively rel ated to BMD of lumbar spine in PHP patients. Conclusions: These results suggest that PTH stimulates bone turnover in PHP Ib patients, resulting in a relatively lower BMD in PHP Ib patients than i n IHP+OHP patients. The present study indicates that bones of most cases of PHP could respond to PTH.