Relationship between increased endogenous parathormone levels and bone density in postmenopausal women treated with bisphosphonates

Bisphosphonates increase bone mineral density (BMD) and also increase parathyroid hormone (PTH): the rule of increased PTH on BMD is not well known. The aim of our study was to assess the relationship between endogenous PTH levels and BMD after 18 months of antiresorptive therapy in a group of post-menopausal women with normal baseline PTH levels. A retrospective study was conducted on 62 women with normal baseline PTH levels (mean age 62.7 +/- 8.6 years) who underwent dual-energy X-ray absorptiometry, thoraciclumbar radiography, and blood and urine sampling at the baseline and after 18 months. All patients were treated with bisphosphonates and received calcium and vitamin D3 supplementation. In the whole group, after 18 months, mean BMD improved both at lumbar spine (0.53 +/- 0.09 vs. 0.49 +/- 0.09 g/cm(2); P<0.05) and at femur (0.66 +/- 0.08 vs. 0.65 +/- 0.09 g/cm(2); P<0.05); PTH levels (56.80 +/- 19.07 vs. 48.74 +/- 14.99 pg/mL; P<0.001) and serum 25-hydroxyvitamin D (60.73 +/- 29.87 vs. 49.81 +/- 26.56 ng/mL; P<0.05) increased. Dividing the patients according PTH variation (>0 or 50), the group with Delta PTH>0 had higher percentage increase of BMD at spine (8.0 +/- 9% vs. 4 +/- 7.5 %; P<0.001) and at total hip (3 +/- 9% vs. 0.49 +/- 8.9%; P<0.001) while the bone alkaline phosphatase significantly decreased (-11.80 +/- 2.19 vs. -4.05 +/- 3.08 ug/L; P<0.001) than the other group. Increased endogenous PTH levels seems to be associated with a higher BMD increase in patients treated with bisphosphonates for postmenopausal osteoporosis. The increase of PTH must be clarified by further investigations