The effect of androgen treatment on bone metabolism in female-to-male transsexuals.

Histomorphometry was performed in iliac crest biopsies from 15 female-to-male (F-M) transsexuals with a mean age of 30 +/- 6.1 (SD) years. At the time of study, they had been treated with parenteral testosterone esters (250 mg/2 weeks) or oral testosterone undecanoate (160 mg/day). The median androgen treatment duration was 39 months. The patients had undergone hysterectomy and bilateral ovariectomy. The bone biopsy was obtained after double tetracycline labeling. Histomorphometric results were compared with data from 8 postmenopausal women and with data from 11 healthy men who had died suddenly. Dynamic parameters were compared with data from the literature. The biochemical picture was characterized by serum testosterone concentrations lower than in eugonadal men and estradiol concentrations lower than in eugonadal women and elevated gonadotrophin levels. The bone mineral density in the F-M transsexuals was as expected for age (Z-score -0.31 +/- 1.49). Cortical thickness was significantly higher in F-M transsexuals than in both control groups. Trabecular bone structure was similar in F-M transsexuals and both control groups. The bone formation parameters were generally lower in F-M transsexuals than in the control groups. The eroded surface was lower in F-M transsexuals than in postmenopausal women. The low bone turnover and preservation of trabecular bone is consistent with the assumption that testosterone treatment protects the bone in these F-M transsexuals from the deleterious effects of estrogen deficiency. The increased cortical thickness suggests an anabolic effect of the testosterone treatment.