Optimizing Thyroxine Dosage After Total Thyroidectomy: Understanding the Factors at Play

Total thyroidectomy is evolving as the choice of treatment for non-malignant thyroid conditions. Therefore, an ideal method of thyroxine replacement is necessary to avoid the ill effects of under- and over-replacement in such patients.

To assess the correlation between optimal thyroxine dose and potential variables like lean body mass (LBM), body surface area (BSA), body mass index (BMI), body weight, age, and sex in patients who underwent total thyroidectomies for benign multinodular goiters in our institute.

A longitudinal cohort study was undertaken at the Government Medical College Thrissur, a tertiary care provider in India, between October 2018 and September 2019. One hundred adult patients who underwent a total thyroidectomy for various benign thyroid conditions were included. They were initially given thyroxine 75 µg upon discharge and received follow-up doses every two months until they achieved euthyroid status on two consecutive visits. The variables evaluated at this stage included age, sex, actual body weight, lean body weight, BMI, and biochemical data (triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH)). Correlation, multiple step-wise regression, and variance were carried out using EPI INFO version 7.2.2.6.

The best predictors for optimum thyroxine dose were BSA (0.923, P < 0.01) and LBM (0.921, P < 0.01), compared with body weight (0.833, P < 0.01) and BMI (0.523, P < 0.01). In our study, the least significant factor was the age of the patient (r = 0.117, P < 0.01). There was no significant association between gender and thyroxine dose. The mean thyroxine dose was 1.87 µg/kg of the patient's body weight.

The optimum thyroxine replacement based on BSA or LBM is a more ideal method than based on BMI or body weight alone.