Effects of thyroxine withdrawal in biochemical parameters and cardiac function and structure in patients with differentiated thyroid cancer.

Aim. Patients with differentiated thyroid carcinoma (DTC) are closely monitored during the first decade after diagnosis. At intervals of 1-2 years withdrawal of suppressive doses of T 4 is recommended in order to check thyroglobulin (Tg) levels under increased TSH. T 4 therapy is usually withdrawn for 5 weeks (during the first 3 weeks patients receive treatment with T 3 instead of T 4 , and the last 2 weeks stop all medication). There are a few reported studies looking into the effects of T 4 withdrawal in athyreotic patients in terms of biochemical parameters and ultrasound indices. We studied patients with DTC at two time points: during suppressive T 4 treatment and at the end of the T 4 withdrawal protocol in order to identify acute changes that become apparent after 5 weeks of treatment modification. Methods. Hormonal and biochemical parameters were measured as well as ultrasound indices of cardiac function and structure. Results. Statistically significant increases were found in total cholesterol, low density lipoprotein (LDL) and high density lipoprotein (HDL) cholesterol and triglycerides with T 4 withdrawal. Creatine phosphokinase showed a striking increase with treatment withdrawal. In addition, liver enzymes, total protein and albumin concentrations increased. Creatinine levels increased significantly and sodium decreased on stopping T 4 treatment. The ultrasound indices of cardiac function and structure did not show significant changes. Conclusion. Acute hypothyroidism following T 4 withdrawal in DTC patients leads to important biochemical changes without significant alterations in cardiac function and structure. These changes may adversely affect patients, especially older patients or those with other chronic diseases.