Dr Shimaoka correctly notes that metastatic cancer may cause hyperthyroidism with low radioactive iodine uptake. However, this is rare and seldom a diagnostic problem. The patients usually have widespread disease and do not survive long.1 The radioactive iodine uptake is low because discharged thyroid hormone suppresses pituitary thyroid-stimulating hormone (TSH) release. After parenteral TSH administration, the image will demonstrate the size and sites of uninvolved areas of thyroid tissue, findings quite dissimilar to those of subacute thyroiditis. Unfortunately, Dr Shimaoka did not perform this study.2 Also, his patient's return to normal thyroid status contrasts sharply with the persistent thyroid involvement characteristic of metastatic cancer. Perhaps a remarkable recovery is possible with lymphoma, but I agree with Dr Shimaoka that the thyroid findings he reported are identical to those seen with spontaneously resolving silent subacute thyroiditis (or silent chronic thyroiditis, as some readers may prefer). This patient might have
Hamburger JI. Thyrotoxicosis due to Metastatic Involvement of the Thyroid-Reply. Arch Intern Med. 1980;140(2):285. doi:10.1001/archinte.1980.00330140143051
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