Thyrotoxicosis due to "silent" thyroiditis.

3 patients (2 male, 1 female) presented with symptoms of thyrotoxicosis associated with elevated blood-levels of thyroid hormone and a markedly depressed thyroidal uptake of 131-I. The male patients (aged 59 and 47) each had a cardiac arrhythmia, but did not have any thyroid pain or swelling. The female with a goitre had no discomfort in the neck. Thyrotoxicosis factitia was excluded by history. The subsequent course of their disease was typical of subacute thyroiditis. The elevated thyroid-hormone levels spontaneously fell to normal over a few weeks. In 1 patient, however, chemical hypothyroidism developed. These patients could have been diagnosed as having hyperthyroidism, rather than subacute thyroiditis, since thyroid pain--and swelling in 2 of the cases--was absent. The correct diagnosis was suspected only after finding a thyroidal uptake of 131-I near zero. The thyroidal uptake of 131-I is still important as a routine diagnostic aid in thyroid disease.