Levothyroxine therapy initiated in nearly 40% of euthyroid adults after hemithyroidectomy within two years

Hemithyroidectomy is often chosen over total thyroidectomy to preserve residual thyroid function and avoid lifelong thyroid hormone replacement therapy. However, a significant proportion of patients still develop hypothyroidism requiring intervention. Understanding the actual burden, timing, and specific predictors of levothyroxine initiation post-surgery is crucial for accurate preoperative counseling and patient expectation management. This study addresses the gap in quantifying the long-term need for thyroid hormone therapy in previously euthyroid individuals undergoing this procedure, particularly identifying high-risk subgroups.

This retrospective population-based cohort study utilized de-identified electronic health record data from Clalit Health Services (2003-2020) via the MDClone research platform. Researchers included 8,467 adults who underwent hemithyroidectomy, had a preoperative TSH < 5.0 mIU/L, no prior thyroid hormone therapy, and at least two years of follow-up. The primary endpoint was the first levothyroxine dispensing or diagnosis of overt biochemical hypothyroidism within 24 months post-surgery. Statistical analysis included multivariable logistic regression to identify predictors of treatment initiation.

Among the 8,467 eligible patients, 3,362 (39.7%) initiated thyroid hormone therapy or developed overt hypothyroidism within 24 months. A substantial portion, 2,179 (25.7%), reached this endpoint within just 4 months, and 3,100 (36.6%) by 12 months. Extended follow-up revealed 558 additional initiations, bringing the cumulative rate to 46.3%. The need for treatment was significantly higher in patients with thyroid cancer (72.7%) compared to those without (33.4%).