Risk factors and timing of postoperative hypothyroidism onset following hemithyroidectomy

This study aimed to identify prognostic factors for postoperative hypothyroidism and assess the timing of its onset in patients who underwent hemithyroidectomy for thyroid tumors. Despite normal preoperative thyroid function, some patients develop postoperative hypothyroidism, necessitating lifelong thyroid hormone replacement therapy. Identifying risk factors and establishing appropriate follow-up guidelines are essential for optimizing patient management.

A retrospective analysis was conducted on 306 patients with normal preoperative thyroid function (thyroid stimulating hormone [TSH]: 0.61-4.23 mIU/L, fT4: 0.93-1.7 ng/dL) who underwent hemithyroidectomy between 2016 and 2021. Patients with prior thyroid surgery or hormone therapy were excluded. Postoperative thyroid function was assessed for at least 2 years.

Postoperative hypothyroidism occurred in 166 patients (54.2 %), with 68.7 % detected within 1 month and 95.2 % within 1 year. Multivariate analysis identified preoperative TSH levels (P = 1.60 × 10⁻¹⁵) and dual positivity for thyroid peroxidase antibody and thyroglobulin antibody (P = 0.0431) as significant predictors of postoperative hypothyroidism. The optimal preoperative TSH cutoff for distinguishing euthyroid and hypothyroid groups was 1.82 mIU/L (area under the receiver operating characteristic curve = 0.875). A clinically applicable threshold of 2.0 mIU/L was determined, with 90.1 % of patients above this level developing hypothyroidism, and 29.7 % requiring thyroid hormone replacement therapy. In contrast, only 3 % of patients with preoperative TSH <2.0 mIU/L required hormone therapy, suggesting the necessity of intensive monitoring in this group.

Preoperative TSH levels and the positivity of both anti-TPO and anti-Tg antibodies were associated with postoperative hypothyroidism, suggesting that they may serve as prognostic predictors for postoperative thyroid dysfunction. Patients with preoperative TSH ≥2.0 mIU/L require careful follow-up, whereas intensive monitoring is unnecessary for those with TSH <2.0 mIU/L. Given that 95.2 % of hypothyroidism cases occur within the first year, thyroid function should be monitored for at least 1 year postoperatively. Additionally, patients developing hypothyroidism within the first year should be followed for up to 3 years to ensure appropriate management.