Bone mineral density and bone microarchitecture after long-term suppressive levothyroxine treatment of differentiated thyroid carcinoma in young adult patients

Bone mineral density (BMD) seems not to be decreased in young patients given long-term suppressive doses of levothyroxine (LT₄), but information regarding the bone microstructure in these patients is lacking. The aim of this study was to determine whether supraphysiologic doses of LT₄, initiated during childhood or adolescence for treatment of differentiated thyroid carcinoma (DTC), have any detrimental effects on bone microarchitecture as evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT). Seventeen patients (27.3 ± 7.1 years old) with DTC with subclinical hyperthyroidism since adolescence and 34 healthy volunteers matched for age, sex, and body mass index were studied by dual-energy X-ray absorptiometry (DXA) to determine the areal BMD at the lumbar spine, hip, and proximal third of the radius. Volumetric BMD and structural parameters of the trabecular and cortical bone were assessed by HR-pQCT of the distal radius and distal tibia. DTC patients were given suppressive doses of LT₄ starting at a mean age of 12.6 years, and the mean duration of treatment was 14.2 years. In DTC patients, clinical parameters did not correlate with DXA or HR-pQCT parameters. No differences were found between the patients and controls with respect to BMD and Z scores at any site evaluated by DXA, and no differences were found in the bone microstructure parameters evaluated by HR-pQCT. This cross-sectional study suggests that long-standing suppressive therapy with LT₄ during the attainment of peak bone mass may have no significant adverse effects on bone density or microarchitecture.