Thyroid Hormone Treatment for Differentiated Thyroid Carcinoma: What Drug, How Long, What Dose?

Abstract: Treatment with thyroid hormone is needed in patients with differentiated thyroid carcinoma (DTC) after the initial treatment (thyroidectomy followed, in most cases, by radioiodine remnant ablation) for two reasons: a) Correction of hypothyroidism in an athyreotic patient ( replacement therapy ); b) Blockade of thyrotropin (TSH) secretion in view of the TSH-dependence of DTC ( TSH-suppressive therapy ). Levothyroxine (L-T4) is the hormone of choice, since combina-tion with levotriiodothyronine does not add any clear advantage with respect to L-T4 monotherapy. While replacement therapy obviously is a lifelong requirement, duration of TSH-suppressive therapy depends on the tumor risk stratification after and the response to the initial treatment. According to recent European and American guidelines, in low-risk DTC L-T4 treatment should be carried out at TSH-suppressive doses until there is evidence that the patient is disease-free. In high-risk DTC, TSH suppression should be maintained for several years after such an evidence has been achieved. After-wards, the patient can be shifted to replacement doses, also to avoid the risks of iatrogenic thyrotoxicosis, especially in the elderly and/or in the presence of cardiovascular disease. The dose of L-T4 must be invidualized; particular attention must be given to the coexistence of pathophysiological conditions or drug treatments that may affect L-T4 absorption or me-tabolism.