Ten-year estimated risk of bone fracture in women with differentiated thyroid cancer under TSH-suppressive levothyroxine therapy

Introduction: After thyroidectomy and radioiodine therapy, patients with differentiated thyroid cancer (DTC) are indefinitely treated with levothyroxine (L-T4). Osteoporosis is a debated consequence of hypothyroxinaemia. The aim of this study was to evaluate bone mineral density (BMD) and fracture risk assessed by FRAX in a cohort of DTC women. Material and methods: Seventy-four women with DTC (aged 56.5 ± 9.9 years) treated at the mean age of 51.9 ± 12.0 years were studied. Baseline BMD and FRAX were evaluated after 3.0 years (median). BMD and FRAX were further evaluated 5.5 years (median) after the baseline evaluation. A cohort of 120 euthyroid women, matched for age, BMI, and menopausal status, were evaluated as controls. Results: L-T4 dosages were 813.6 ± 208.8 μg/week and 782.1 ± 184.4 μg/week at the baseline and second evaluation, respectively. The risks of major osteoporotic fracture (MOF) and hip fracture (HF) were similar in DTC patients and in controls. In DTC women, significant changes in FRAX were found, with a higher increase in the probability of HF than of MOF. A similar change was found in controls. A significant inverse correlation (P < 0.001) between L-T4 dosage and HF/MOF probability on both first and second evaluations was found. A significant inverse correlation (P = 0.05) was found between fT4, TSH and duration of therapy and HF/MOF probability only on the second evaluation. Conclusions: FRAX increase is a multi-factorial, age-related phenomenon. The absence of correlations between L-T4 dosage, length of therapy or fT4 levels and FRAX does not enable us to attribute an increased fracture risk to DTC women with well-controlled disease on therapy. (Endokrynol Pol 2016; 67 (4): 350–358)