Optimization of thyroxine replacement therapy after total or near-total thyroidectomy for benign thyroid disease

Background: Total or near-total thyroidectomy is increasingly used to treat benign thyroid conditions. Lifelong treatment with thyroxine (T4) is then required, but the optimal dose is difficult to predict. This study investigated factors that might predict the ideal T4 dose, with the aim of reducing delays in achieving normal thyroid function after surgery. Methods: Data on 98 patients who underwent total or near-total thyroidectomy for benign disease were reviewed retrospectively. Patient and operative variables that might predict time to achieve normal thyroid function and optimal T4 replacement dose were examined. These data were then used to formulate an algorithm for T4 dosage, based on patient weight, that was subsequently applied prospectively to a comparable group of 27 patients. Results: The median time to achieve normal thyroid function was 14.5 (range 2-120) weeks before introduction of the algorithm, and was greater in patients needing large changes in T4 dose. In multivariate analysis, the best predictors of optimal T4 dose were bodyweight (r = 0.46, P < 0.001) and age (r = -0.32, P = 0.002). Subsequent use of a weight-related algorithm improved time to achieve normal thyroid function. Conclusion: The T4 replacement dosage after total or near-total thyroidectomy is largely influenced by bodyweight. Use of a weight-related algorithm improves patient care compared with use of standard T4 dose-titration methods.