Therapy of male osteoporosis with parathyroid hormone

Definable causes of male osteoporosis account for only about 60% of the osteoporotic population. Those for whom no etiology is readily apparent are said to have primary or idiopathic male osteoporosis. In these individuals, histomorphometric studies indicate that this is a disorder that is more typically characterized by low turnover. Although antiresorptive agents such as alendronate have been shown to increase bone mass in men, the rationale for an anabolic agent that can stimulate bone formation is clear. The most attractive anabolic agent at this time is parathyroid hormone (PTH) administered in low dosage and intermittently. Such regimens in experimental animals have been associated with marked gains in bone mass. Slovik et al. showed that parathyroid hormone can increase vertebral bone mass in men with idiopathic osteoporosis. We have conducted the first controlled, randomized, double-blind study of PTH in men with idiopathic osteoporosis. Twenty-three men, 30-68 years old (50 +/- 1.9) with Z-scores less than -2.0 were assigned to a placebo (n = 13) or treatment (n = 10) arm. After 18 months, those who received PTH showed a 13.5 +/- 3% increase in bone mass, significantly greater than the placebo group whose bone density did not change. Femoral neck bone density increased significantly by 2.9 +/- 1.5%. The distal radius site did not change. During an open label extension for an additional 12 months, there was no further increase in bone density in the lumbar spine but the femoral neck continued to show gains. Markers of bone formation and resorption increased in the PTH arm reaching a peak between 9 and 12 months of therapy and declining thereafter. Parathyroid hormone was well tolerated. These results suggest that low-dose intermittent PTH may be an efficacious therapy for men with idiopathic osteoporosis.