Spinal and peripheral bone mineral densities in acromegaly: the effects of excess growth hormone and hypogonadism.

STUDY OBJECTIVE: To measure spinal and peripheral bone mineral densities in patients with acromegaly.

DESIGN: Retrospective study.

SETTING: Tertiary care center.

SUBJECTS: Twenty-four patients with acromegaly and 24 case controls. Seventeen patients (12 eugonadal and 5 hypogonadal) had "active" disease as indicated by elevated plasma concentrations of growth hormone or somatomedin C or both at the time of the study. Seven patients (all hypogonadal) had inactive disease by these criteria.

MEASUREMENTS AND MAIN RESULTS: Bone mineral was measured by single photon absorptiometry of the forearm and dual photon absorptiometry of the spine. The forearm bone mineral content of patients with active disease, regardless of gonadal status, was significantly higher than that of normal subjects (P less than 0.001) or of patients with inactive disease (P less than 0.001). The disease "activity" (17.2 +/- 3.7; CI, 9.5 to 24.9) and the sex of the patient (female, -16.6 +/- 3.4; CI, -23.7 to -9.5) were the only independent predictors of forearm measurements. Vertebral bone densities were lower in acromegalic patients than in normal subjects (P less than 0.001). Vertebral values were correlated with the gonadal status of the patients (hypogonadism, -0.126 +/- 0.056; CI, -0.244 to -0.009) and with serum calcium concentrations (0.592 +/- 0.274; CI, 0.032 to 1.153) but not with acromegalic activity. In 13 patients, forearm bone was measured before and after treatment (mean duration of follow-up, 3.4 years). Patients with persistently elevated, plasma somatomedin C concentrations at the end of the study period showed a mean annual increase of 1.5% in forearm measurements during the period of observation, whereas patients with normal concentrations showed a mean annual decrease of 1.0% (P less than 0.01 for the difference between the groups). The percent change in forearm bone mineral content per year (y) was highly correlated with residual somatomedin C activity (x): y = 2.023x - 2.75; r = 0.665.

CONCLUSIONS: Forearm and vertebral bone mineral measurements change in opposite directions in acromegaly. The high forearm values are attributable to the growth-promoting action of growth hormone and somatomedin C, whereas low vertebral values are associated with hypogonadism.