Variable bone mass recovery in hyperthyroid bone disease after radioiodine therapy in postmenopausal patients.

Objectives: Long-term follow-up of postmenopausal hyperthyroid females after radioiodine therapy, since hyperthyroidism is known to cause impressive bone loss which may increase the risk of bone fractures.

Methods: Bone mineral density (BMD) and biochemical parameters of bone metabolism in hyperthyroid postmenopausal patients were investigated before and 2 years after radioiodine therapy and compared with euthyroid age-matched controls.

Results: At baseline, the incidence of low BMD with t-scores more than 2.5 S.D. below normal was significantly higher in hyperthyroid patients (54%) than in controls (20%, P<0.001). Regardless of initial BMD values, osteocalcin (OC) was also higher in all hyperthyroid patients (P<0.0001). After 2 years, all treated patients were euthyroid and OC levels were in the upper normal range. In hyperthyroid patients with initially low BMD, bone density values had increased significantly by +6.5% (P<0.008) as compared with baseline values. In contrast, hyperthyroid patients with initially normal BMD showed a further decrease in lumbar BMD values of -4.3% despite radioiodine treatment. BMD in euthyroid controls decreased by -6.5% within 2 years.

Conclusions: We conclude that hyperthyroid postmenopausal patients with generally increased bone turnover may show individual differences in bone loss and BMD recovery after radioiodine treatment. The mechanisms for this variable manifestation of osteoporosis have still to be elucidated, since this has implications for prophylactic and therapeutic strategies in these elderly patients.