Influence of Thyroid Hyperfunction on Bone System Changes

Introduction. Bone density measurements during the last decade have demonstrated that bone loss is common in patients with overt hyperthyroidism and to a lesser extent in those with subclinical hyperthyroidism, whether caused by nodular goiter or excessive doses of thyroid hormone. Overt hyperthyroidism is associated with accelerated bone remodeling, reduced bone density, osteoporosis, and an increase in fracture rate. The bone density changes may or may not be reversible with therapy. These changes in bone metabolism are associated with negative calcium balance, hypercalciuria and, rarely, hypercalcemia. Aim. To investigate frequency and structure of bone disease in patients with thyrotoxicosis, and also to find out the features of clinical manifestations of osteoporosis, taking into account the duration of disease. Materials and methods. 65 patients with thyrotoxicosis syndrome were included. The bone density based on the T-score of femoral neck and lumbar vertebrae were compared between three groups. For densitometry, dual-energy X-ray absorptiometry was used to measure the bone density in lumbar vertebrae (L1–L4, anterior-posterior measurements) and femoral neck. The measurement was performed by an expert technician using densitometer Lunar Prodigy Primo, General Electric, USA. A complete set of data was collected for each patient and include: Patient's age, history of hypothyroidism or other chronic diseases, weight, height, body mass index (BMI), T-score data of lumbar, and femoral neck densitometry, calcium, phosphorus, alkaline phosphatase, Vitamin D and TSH levels and duration of hypothyroidism. The Ethics Committee of the Bukovinian State Medical University approved this study, and a written informed consent was obtained from all study participants. Data of 65 individuals was analyzed using the regression analysis, analysis of variances and Mann-Whitney (for non-parametric quantitative data) tests. Continuous variables were summarized using means and standard deviation; frequencies and percentages were used to summarize categorical variables. A p < 0,05 was considered statistically significant. Results and discussion. Indexes of bone mineral density was decreased, and frequency of osteoporosis and osteopenia was higher as compared to population indexes in persons of corresponding age. Osteoporosis in one of two basic localizations is lumbar department (L1–L4) and proximal femur was found in 4 patients (6.2 %), osteopenia – in 29 (44.6 %). On the whole the decline of bone mineral density was observed in 33 (50.8 %) patients. Correlation analysis showed statistically significant negative correlation between mineral bone density and age of patients (r = -0.42, р < 0.05), and also weak correlation with the thyrotoxicosis duration (r = -0.18; р < 0.05). Positive correlation was found between mineral bone density and height (r = 0.27; р < 0.05), body mass index (r = 0.29; р < 0.05), and also between the free thyroxine level and mineral bone density (r = 0.19). Conclusions. The expressed unfavorable influence of thyroid hormones high levels is set on bone mineral density. Analysis of bone metabolism markers showed the acceleration of bone resorption. There were significant correlation between the free thyroxine high levels and the markers of bone mineral density. Duration of thyrotoxicosis syndrome had negative correlation with indexes of bone mineral density. During thyrotoxicosis decompensation there is an acceleration of bone exchange, that was confirmed by the significant correlation between the free thyroxine levels and C-terminal peptide.