BACKGROUND
The thyroid gland is a butterfly shaped organ located in the front of the neck. This gland produces an important hormone, called thyroid hormone, that helps control a person’s metabolism (how the body uses energy). Hypothyroidism occurs when thyroid hormone levels are low and/or TSH levels are high. Hypothyroidism is treated by a thyroid pill, usually levothyroxine.

There are a number of thyroid diseases, both cancerous and noncancerous, which are treated with surgery to remove all, or part, of the thyroid gland. If a person has their entire thyroid gland removed during surgery (total thyroidectomy), the body will no longer be able to produce thyroid hormone and the person will become hypothyroid, requiring a thyroid hormone replacement pill (levothyroxine) every day for the rest of their lives. On the other hand, sometimes only part of the thyroid gland may be removed during surgery (partial thyroidectomy or thyroid lobectomy), in which case the thyroid tissue left behind after surgery might produce enough thyroid hormone to meet the body’s needs. If this is the case, levothyroxine will not be needed after surgery. Not everyone who has part of their thyroid left behind after thyroid surgery, however, will make enough thyroid hormone and such people will need to take a thyroid hormone pill. Unfortunately, it is difficult to predict if a thyroid hormone pill will be needed after partial thyroid removal for people with normal thyroid hormone levels before thyroid surgery. For this reason, the goal of this study was to develop a model to help predict which people will need to take a thyroid hormone pill after partial thyroidectomy.

THE FULL ARTICLE TITLE
Mimouni E, et al. A clinical risk score for thyroid hormone therapy after partial thyroidectomy. J Surg Res 2025;314:169-175.

SUMMARY OF THE STUDY
The study authors reviewed the medical records for all patients who underwent partial thyroidectomy at their institution between 2013 and 2020. They identified 425 patients who met study criteria. The authors then identified which of these patients were prescribed levothyroxine after surgery. The authors then re-reviewed each patient in the study group to see if there were any consistent characteristics that might predict which patients would need to take levothyroxine after surgery and which patients would not.

Finally, using the identified characteristics, the authors employed statistical tools to develop a scoring system for predicting the need for a thyroid hormone pill after partial thyroid removal.

Of the 425 patients in the study, 101 (23.8%) had documented postoperative hypothyroidism based on blood testing showing low thyroid hormone levels and/ or an increased TSH, and 178 (41.9%) were prescribed levothyroxine after partial thyroidectomy. The researchers identified the following characteristics as strong predictors of needing to take a thyroid hormone pill after surgery: 1) non-Black race, 2) TSH >1.59 before surgery, 3) Hashimoto’s thyroiditis and 4) surgery performed to treat thyroid cancer.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This data identifies characteristics that make it more likely that a patient will require levothyroxine replacement after a partial thyroidectomy/lobectomy. Although the model developed from this study does not perfectly predict who will need to take levothyroxine after partial thyroidectomy, it can suggest which patients might have this need. For this reason, this model might be useful in helping patients who are planning partial thyroidectomy understand what to expect after surgery.

It is important to acknowledge that there are some features of this study that limit its usefulness. Only one institution was included in the study, and the data were collected from old medical records, some of which may not be complete. This means that the results of the study may not apply to the broader general population, which may be different from the study group. In addition, the identification of the characteristic of “non-Black race” may actually be the result of biases related to how people of different races and/or economic backgrounds seek and receive health care, rather than a true predictor of need for thyroid hormone after partial thyroidectomy. For these reasons, further research and refinement are needed to accurately predict which patients undergoing partial thyroid removal will need a thyroid hormone pill after surgery.

As with all models related to calculating treatment risks, the model described here represents only one part of the pre-surgery discussion. These models can be used to guide or provide estimations of risk, but they all have a degree of error and every patient is unique. Before proceeding with any surgery, it is important for patients and their surgeons to have detailed conversations involving shared decisions making and clear discussions of what can be expected after surgery.

— Katelyn Larson, MD and Jason D. Prescott, MD PhD

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