[T3 hyperthyroidism with metastatic follicular thyroid carcinoma in substitution therapy]

This case report shows the anamnesis of a female patient with follicular Thyroidglandular-Ca. in an advanced stage with multiple metastases in the skeletal system, lungs and hilar lymph nodes. In addition, the patient showed a T3 hyperthyroidism with clinical symptoms but normal to low level of T4. After exclusion of hormone producing metastases as a reason for the hyperthyroidism, the most likely explanation would be an increased 5'-deiodination from T4 to T3.