Bone metabolism during anti‐thyroid drug treatment of endogenous subclinical hyperthyroidism

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Abstract
There is recent evidence that both exogenous and endogenous subclinical thyrotoxicoses are associated with decreased bone mineral density. Scanty information is available on bone metabolism in these conditions when euthyroidism is restored. We evaluated the effect of anti-thyroid drug treatment on bone metabolism in endogenous subclinical hyperthyroidism. Prospective follow-up study over 2 years during treatment with methimazole, with an untreated control group. Sixteen post-menopausal women with endogenous subclinical hyperthyroidism associated with multinodular goitre, eight of whom were treated with methimazole. Serum concentrations of free T4, total T3, TSH, osteocalcin, urinary excretion of hydroxyproline and forearm bone mineral density were measured at regular intervals. Significant changes in serum osteocalcin concentration or urinary hydroxyproline excretion were not observed in either group. Distal, but not proximal, forearm bone mineral density, expressed as a percentage of the base-line value, was significantly (P < 0.05) higher in the treated than in the untreated subjects in the second year of treatment. Treatment with methimazole in post-menopausal women with endogenous subclinical hyperthyroidism associated with multinodular goitre can prevent excessive loss of bone, at least in the distal forearm.