Metastatic thyroid cancer presenting as thyrotoxicosis: report of three cases

Three patients with metastatic thyroid follicular carcinoma developed thyrotoxicosis. Two had mild T3 toxicosis without detectable TSH binding inhibitor immunoglobulins (TBII) or thyroid stimulating antibodies (TSAb). Considerable concentration of 131I by tumours occurred, although serum TSH was undetectable. The third patient developed thyrotoxicosis several months after treatment with 131I had commenced and this was associated with concurrent increase in both TBII (90%; normal, less than 11%) and TSAb (2100%). We conclude that thyrotoxicosis in patients with metastatic thyroid carcinoma may result from a large bulk of tumour functioning either autonomously or after stimulation by TSH receptor antibodies.