Objective:

To assess the initiation of thyroid hormone therapy following hemithyroidectomy in patients with previously normal thyroid function.

Approach:

• Study Design: A retrospective population-based cohort study using de-identified electronic health record data from Clalit Health Services in Israel, including 8,467 adult patients who underwent hemithyroidectomy between 2003 and 2020.
• Primary Endpoint: Initiation of thyroid hormone therapy within 24 months, defined as the first dispensing of levothyroxine or development of overt biochemical hypothyroidism.
• Exploratory Analysis: Assessment of treatment initiation beyond 24 months and identification of associated factors.

Key Findings:

• 40% of patients initiated thyroid hormone therapy within 24 months post-surgery.
• 26% initiated therapy within the first 4 months, and 37% within the first 12 months.
• An additional 558 patients initiated therapy during extended follow-up, raising the cumulative rate to 46%.
• Treatment initiation was more common in patients with thyroid cancer (73%) compared to those without (33%).
• Each 1 mIU/L increase in preoperative TSH level was associated with 1.6 times the odds of treatment initiation.

Interpretation:

Thyroid hormone therapy initiation is common after hemithyroidectomy, particularly among patients with higher preoperative TSH levels and those with thyroid cancer.

Limitations:

• The primary endpoint reflects treatment initiation rather than permanent dependence on thyroid hormone.
• Specific indications for levothyroxine could not be determined, especially in thyroid cancer patients.
• Causality could not be established, and important clinical variables were unavailable.

Conclusion:

Thyroid hormone therapy initiation after hemithyroidectomy is common, affecting 39.7% of previously euthyroid adults within 2 years and 46.3% over extended follow-up. Preoperative TSH levels and thyroid cancer identify high treatment burden subgroups.

Sources:

• Endocrine