Longitudinal changes in lumbar bone density among thyrotoxic patients after attainment of euthyroidism

Hyperthyroidism increases bone turnover, which, in turn, may lead to bone loss from the spine and hip. Treatment of thyrotoxicosis may restore bone mass, but there are few long term prospective studies. We examined lumbar bone mineral density (BMD) in 21 subjects [11 with hyperthyroidism (HT) and 10 controls of similar age] by dual photon absorptiometry in 1986 and by dual energy x-ray densitometry in 1991. All 11 HT patients were successfully treated and remained euthyroid (mean TSH, 2.25 +/- 0.80 mU/L) for more than 3 yr. Lumbar BMD increased 11.03 +/- 2.38% (P < 0.001) in HT patients, but only 2.6 +/- 2.15% (P = 0.10) in control subjects. Among HT patients, the higher the T3 concentration during hyperthyroidism, the greater the subsequent increase in lumbar BMD (r = 0.72; P < 0.03). Age at treatment, in contrast, was not a significant predictor of eventual spinal bone mass. In conclusion, successful treatment of hyperthyroidism produced a significant increase in lumbar BMD. Hence, bone loss associated with thyrotoxicosis may not be permanent. Future work designed to examine the effect of thyroid hormone on skeletal homeostasis should include large scale longitudinal studies of both men and women.