We report a patient with unilateral thyroid carcinoma, who developed h
yperfunction of the thyroid gland during the metastatic progression of
the thyroid carcinoma. Concurrently with this event, TSI increased an
d it is suggested that the differentiated aggressive metastatic thyroi
d neoplasm had initiated the autoimmune disorder leading to TSI produc
tion and thus to hyperplasia and hyperfunction of the thyroid resultin
g in hyperthyroidism.