Endocrine Abstracts

Introduction: Osteoporosis and vertebral fractures (VFs) commonly occur in overt and subclinical primary hyperthyroidism. In this clinical setting, bone damage is caused by the direct effects of thyroid hormone in excess on bone remodeling, although there is also evidence that low thyrotropin (TSH) values may play a role in driving fracture risk. In fact, TSH was shown to have direct inhibitory effects on osteoclastogenesis and bone resorption. Based on these data, one could argue that primary and secondary hyperthyroidism may induce variable effects on bone in relationship to the different TSH values. In this cross-sectional study, we evaluated for the first time the prevalence and determinants of VFs in patients with TSH-secreting pituitary adenoma (TSH-oma).

Patients and Methods: Twenty-two patients (10 M, 12 F; median age 47.0 years) with TSH-oma were retrospectively evaluated for clinical and biochemical parameters as well as for thoracic VFs using a morphometric approach on lateral chest X-ray routinely performed in the pre-surgical diagnostic work-up.

Results: At the time of VFs assessment, 17 patients (77.3%) had an overt hyperthyroidism and five patients (22.7%) had thyroid hormone values in the reference ranges. TSH values were inappropriately normal in 17 patients and high in five patients. VFs were found in 13 patients (59.1%) in association with older age (P=0.007) and higher serum free-thyroxine (FT4) values (P=0.02). The prevalence of VFs was more frequent in patients with overt hyperthyroidism as compared to those with thyroid hormones in the reference ranges (70.6% vs. 20.1%; P=0.04), whereas no significant difference was found in patients with high vs. normal TSH values (P=0.38).

Conclusions: This study provides for the first time evidence that patients with TSH-oma may develop VFs in close relationship with the severity of hyperthyroidism. It is likely that elevated TSH levels do not protect bone in TSH-omas due to the predominant negative effect on bone of elevated circulating thyroid hormones.