Transient thyrotoxicosis in a patient with a functioning nodule; a possible occurrence of silent thyroiditis

A 48-year-old woman with diffuse goiter presented with typical symptoms and signs of thyrotoxicosis. Thyroid scanning with I-123 revealed a localized accumulation of the radionuclide in the left lobe which corresponded to a small nodule later detected by ultrasonography, with suppression of the remaining tissues. Owing to the overall reduced radioactivity in the thyroid, she was suspected of having silent thyroiditis causing thyrotoxicosis. Meanwhile, the thyrotoxicosis subsided concurrently with an increase in radioactivity in the extranodular area that had initially been suppressed. The histology of thyroid tissues obtained at the time of operation revealed follicular adenoma or hyperplasia in the area of the localized I-123 uptake and findings similar to those in Hashimoto's thyroiditis in the remaining tissues, supporting our clinical diagnosis of silent thyroiditis together with a functioning nodule.