Low bone mass in hypogonadal males. Effect of testosterone substitution therapy, a densitometric study

Sixteen (16) male patients who were suffering from hypogonadism but who were free from bone symptoms were recruited from the Andrology Clinic. Their bone mineral density (BMD) was assessed by single photon absorptiometry in the non-dominant radius, at both the distal radius (DR) (27% trabecular bone) and the midshaft radius (MR) (90% cortical bone). Measurements were carried out before and during testosterone substitution therapy. BMD was found to be lower in the subjects than in the controls, to a similar extent at both the DR (0.47 ± 0.02 g/cm 2, i.e. 83.1 ± 4.3% of the value in the controls, or Z score −1.42 ± 0.39; P < 0.01) and the MR (0.68 ± 0.02 g/cm 2, i.e. 87.8 ± 2.4% of the value in the controls, or Z score −1.49 ± 0.33; P < 0.01). There was no correlation between testosterone levels and BMD at either the DR or the MR at the beginning of the study. Following testosterone substitution therapy, bone mineral content (BMC) increased significantly at the DR (+5.9 ± 1.4% per year; P < 0.01) and at the MR (+1.1 ± 0.9% per year; P < 0.01). If the study is limited to the subjects who had achieved full bone age maturity before the start of therapy, the bone gain remains significant only at the DR, a site with a sizeable proportion of trabecular bone.