Endocrine Abstracts

Thyroid hormones play an important role in bone metabolism. The potential action of prolonged levothyroxine therapy on bone mass reduction is stil a matter of debate.

The aim of our one year prospective study was to elucidate whether longterm suppressive thyroid hormone therapy in patient with differentiated thyroid cancer (DTC) affects bone metabolism, osteoprotegerin (OPG) and soluble receptor activator of nuclear factor kβ ligand (sRANK-L) and is a risk factor for osteoporosis. Forty-nine patients with DTC (17 premenopausal, 22 postmenopausal women, 10 men) were investigated. All of them had undergone a total thyroidectomy and subsequent I-131 radio-iodine ablation therapy. The levels of free triiodothyronine (fT3), free tetraiodothyronine (fT4), thyrotropin (TSH), parathormone (PTH), serum calcium (Ca), phosphorus, alkaline phosphatase (ALP), osteocalcin (OC), OPG, sRANK-L, urinary deoxypyridinoline (DPD) and 24-hour urine calcium were assessed before and after one year suppressive thyroid hormone therapy. Bone mineral density (BMD) (g/cm²) in lumbar spine (L1–L4), femoral neck, trochanter and total hip was measured by dual-energy X-ray absorptiometry (DXA) before tratment and after one year of treatment.

In the first year of suppressive thyroid hormone therapy, a statisticaly significant increase was found in serum Ca, ALP, urinary DPD and calcium in each of the three subgroups; and a statisticaly significant decrease was found in serum OPG levels in pre- and postmenopausal groups. No difference was noted in serum sRANK-L before end after one year of treatment in each group. We detected significant decreases at post treatment DXA values in comparison to basal DXA values in lumbar BMD in premenopausal women (1.12±0.10 vs 1.08±0.10, P=0.01) and similarly at post treatment femoral neck BMD (1.12±0.27 vs 1.02±0.16, P=0.02) in men.

In conclusion, the results of our study revealed that longterm suppressive thyroid hormone therapy in patients with DTC may affect bone metabolism and OPG/RANK-L system.