Prolonged suppressive L-thyroxin therapy - Longitudinal study of the L-T4 effect on bone density and bone metabolism markers in 71 patients

OBJECTIVES: A prospective longitudinal study was conducted to investigate t he influence of prolonged suppressive L-thyroxin therapy on bone density an d biochemical markers of bone remodeling. PATIENTS AND METHODS: Seventy-one patients (including 28 menopaused women) taking long-term L-T4 for thyroid carcinoma were divided into 3 groups acco rding to their TSH level: low (TSH < 0.04 mIU/l), moderate (0.04 TSH less t han or equal to 0.10 mIU/l) and high (TSH > 0.10 mIU/l). Bone density was m easured in lumbar vertebrae annually for a mean 4.5 years. Bone metabolism markers were measured over a 4 year period. Bone density measurements of th e femur were also obtained for 2 years in 16 menopaused women. RESULTS: Lumbar bone density did not decline whatever the TSH level or the duration of L-T4 treatment. Likewise for menopaused women without substitut ion estroprogesterone therapy. Over the 4 years, biochemical markers of bon e formation, including bone alkaline phosphatases and osteocalcin, or of bo ne resorption, including urinary hydroxyprolin, did not vary. In addition, in menopaused women, femoral bone density was not significantly lowered ove r the 2 years follow-up. No lumbar or femoral osteopenia was observed in th ese patients taking L-thyroxin, even for those with complete TSH blockade. Biochemical markers did not demonstrate a significant acceleration of bone turnover during prolonged administration of L-T4 at suppressive levels.