Levothyroxine (LT4) is the therapy of choice in patients with post-operative hypothyroidism due to total thyroidectomy for differentiated thyroid carcinoma (DTC). LT4 therapy is necessary to maintain euthyroidism and therefore reduce serum levels of thyroid stimulating hormone (TSH) which could eventually stimulate thyroid tumor cells. Hormonal withdrawal is although requested before the diagnostic 131-Iodine whole body scan (WBS) and before radioiodine (RAI) ablation therapy in order to increase TSH serum levels and stimulate the uptake of 131-Iodine by all thyroid cells. Thyroid hormones play a crucial role in the regulation of several metabolisms and also influence renal and hepatic physiology, consequently thyroid dysfunction affects different metabolisms and also renal and hepatic functions. The aim of the present study was to compare the different metabolic effects of LT4 and liothyronine (LT3) therapy in patients with acute hypothyroidism due to hormonal withdrawal before RAI.
20 patients previously treated with total thyroidectomy for DTC and RAI were involved in the study. Hormonal withdrawal was requested before the diagnostic WBS. All patients underwent at baseline a physical examination and a standard ECG. Blood samples were collected to test thyroid hormonal profile (FT3, FT4, TSH, Tg, Ab-Tg) serum creatinine, total cholesterol, triglycerides, alanine aminotransferase (ALT), aspartate aminotransferase (AST) , creatininchinasi (CPK) at baseline, on day 15 and on day 30. The patients were divided in two groups: group 1 (n = 10) were daily treated with LT4 (125-175 μg) and group 2 (n = 10) were daily treated with LT3 (60 μg).
All baselines blood tests done in hypothyroidism showed no significant differences in the two groups.
On day 15:
• TSH levels were significantly decreased in group 2 compared to group 1 (p< 0,0005);
• Creatinine (p<0.005), total cholesterol (p<0,05), triglycerides (p<0,05), ALT (p<0,05), AST (p<0,05), CPK (p<0,05) values were all significantly decreased in group 2 compared to group 1.
On day 30:
• No significant differences in TSH, creatinine, total cholesterol, triglycerides, ALT, AST and CPK serum levels were observed within the two groups.
Our results suggest that LT3 could be considered the treatment of choice of acute hypothyroidism due to HW before RAI because it allows a more rapid normalization of all the hematological parameters altered by hypothyroidism. LT3 can then be followed by the chronic administration of LT4. This new therapeutic regimen may be particularly important for those patients presenting with an already precarious balance in kidney, cardiac and hepatic metabolisms.