The effects of thyrotropin-suppressing therapy on bone metabolism in patients with well-differentiated thyroid carcinoma.

Studies on the effects of levothyroxine (LT4) therapy on bone and bone metabolism have yielded conflicting results. This 1-year prospective study examined whether LT4 in patients with well-differentiated thyroid carcinoma (DTC) is a risk factor for bone mass loss and the subsequent development of osteoporosis. We examined 93 patients with DTC over 12months after initiating LT4 therapy (early postoperative period). We examined another 33 patients on long-term LT4 therapy for DTC (late postoperative period). Dual energy X-ray absorptiometry was performed at baseline and after 1year. The mean bone losses during the early postoperative period in the lumbar spine, femoral neck, and total hip, calculated as the percentage change between levels at baseline and 12months, were -0.88, -1.3 and -0.81%, respectively. Bone loss was more evident in postmenopausal women (lumbar spine -2.1%, femoral neck -2.2%, and hip -2.1%; all P<0.05). We compared the changes in annual bone mineral density (BMD) in postmenopausal women according to calcium/vitamin D supplementation. Bone loss tended to be higher in the postmenopausal women receiving no supplementation. There was no decrease in BMD among patients during the late postoperative period. The mean bone loss was generally greater in the early than in the late postoperative group, and this was significant at the lumbar spine (P=0.041) and femoral neck (P=0.010). TSH-suppressive levothyroxine therapy accelerates bone loss, predominantly in postmenopausal women and exclusively during the early post-thyroidectomy period.