Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
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HYPOTHYROIDISM
Thyroid hormone dosing after thyroid surgery: Is there a better way?

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BACKGROUND
Thyroid surgery (thyroidectomy) is a common procedure done for cancer as well as benign conditions (nodules, hyperthyroidism, etc). The main byproduct of a thyroidectomy is hypothyroidism, as the thyroid gland gland been removed. Post-surgical hypothyroidism requires thyroid hormone replacement (levothyroxine) after the procedure for the rest of their lives. They may or may not have been on thyroid hormone previously. Calculation of the dose of the levothyroxine to begin after a thyroidectomy can often be a challenge. Frequently, the dose is based on the person’s weight. However, this may be inaccurate.

This study was done to look at the outcome of thyroid hormone replacement in the post-operative period. Either a weight based dosing or a computer assisted algorithm was utilized. The goal of the study was to look for any potential differences in these approaches.

THE FULL ARTICLE TITLE
 Barrio M et al 2023 Computer-assisted levothyroxine dose selection for the treatment of postoperative hypothyroidism. Thyroid 33:547–555. PMID: 37084246.

SUMMARY OF THE STUDY
The authors of the study reviewed ~3000 medical records. Of these, ~900 met criteria for inclusion in the study. Patients either had a total thyroidectomy or a completion thyroidectomy (a second surgery done after an initial partial removal of the thyroid). Most patients were female and a majority had a diagnosis of thyroid cancer.

Dosing of the thyroid hormone based on the person’s weight was accurate approximately 30% of the time. Using the computer assisted dose calculation, the accuracy was 40 to 47%. Patients with obesity and benign thyroid disease and low risk thyroid cancer were more likely to be started on a dose that was too high. On the other hand, women who were on estrogen containing medications as well as men were more often likely to be started on a dose that was too low.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Computer assisted dose calculation of the thyroid hormone dosing can improve the accuracy of the levothyroxine dose calculation following a thyroidectomy procedure. However, other factors such as body weight, other medications and gender also play a role in the response to thyroid hormone therapy after the surgery. It is important to acknowledge and understand these differences so that the need for repeated dose adjustments can be minimized.

— Vibhavasu Sharma, MD, FACE

ABBREVIATIONS & DEFINITIONS

Thyroidectomy: surgery to remove the entire thyroid gland. When the entire thyroid is removed it is termed a total thyroidectomy. When less is removed, such as in removal of a lobe, it is termed a partial thyroidectomy.

Completion thyroidectomy: surgery to remove the remaining thyroid lobe in thyroid cancer patients who initially had a lobectomy.

Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.

Levothyroxine (T4): the major hormone produced by the thyroid gland and available in pill form as Synthroid™, Levoxyl™, Tyrosint™ and generic preparations.

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