Does Radioiodine Treatment Prevent Atrial Fibrillation and Bone Loss in Endogenous Subclinical Hyperthyroidism?

Inclusion Criteria: * Subclinical hyperthyroidism \[TSH ≤ 0.1 mU/L, fT4 and T3 within the normal range of the own laboratory (determined 2 times in own laboratory) with an interval of at least 2 months\]. * Endogenous cause of subclinical hyperthyroidism limited to autonomous adenoma or multinodular goiter (diagnosis made by the attending physician, based on palpation and the result of a thyroid scintigram). * Informed consent. Exclusion Criteria: * Medication with anti-thyroid drugs in the last 3 months (also not allowed during follow-up); thyroid hormone in the last 3 months (allowed during follow-up, but TSH levels should be kept between 0.1 mU/L and the upper limit of normal in the own laboratory); and oral glucocorticoids in the last 3 months (allowed during follow-up when absolutely necessary, but patients in whom glucocorticoids are started cannot be evaluated with respect to changes in bone mineral density \[BMD\]). * Radioiodine therapy in the past. * Iodine-induced subclinical hyperthyroidism. * Pituitary or hypothalamic insufficiency. * Pregnancy. * Age \<= 40 years. * Severe non-thyroidal illness. * Drug abuse. * Unstable angina pectoris, (history of) atrial fibrillation, (history of) congestive heart failure. * (History of) osteoporotic fracture(s). * Patients younger than 70 years of age with a bone mineral density T-score \< - 2.5 standard deviations (SD), or older than 70 years of age with a bone mineral density Z-score \< 1.0 SD. (These patients can be ran…