A large proportion of patients with previously normal functioning thyroids initiated thyroid hormone therapy within 2 years following hemithyroidectomy, with most treatment beginning during the first postoperative year.
Investigators conducted a retrospective population-based cohort study using de-identified electronic health record data from Israel's Clalit Health Services, extracted through the MDClone research platform. The analysis included 8,467 adult patients who underwent hemithyroidectomy from 2003 to 2020, had normal preoperative thyroid function, were not receiving thyroid hormone therapy prior to surgery, and had at least 2 years of follow-up.
The primary endpoint was initiation of thyroid hormone therapy within 24 months, defined as the first dispensing of levothyroxine combination thyroid hormone therapy or the development of overt biochemical hypothyroidism. An exploratory extended analysis assessed treatment initiation beyond 24 months and identified factors associated with initiating therapy.
The investigators noted that 40% (n = 3,362) of the patients reached the primary endpoint. Most treatment initiation occurred early: 26% and 37% of them initiated therapy within the first 4 and 12 months postsurgery, respectively. During extended follow-up, an additional 558 patients initiated therapy, increasing the cumulative treatment burden to 46%. Nearly all endpoint events were identified through drug dispensing rather than biochemical findings alone.
Treatment initiation was more common among patients with thyroid cancer compared with among those without thyroid cancer (73% vs. 33%). Each 1 mIU/L increase in preoperative thyroid-stimulating hormone level was associated with about 1.6 times the odds of treatment initiation. Younger age, residence outside middle or peripheral regions, and hypertension were also independently associated with treatment initiation.
About 92% of treatment initiation events occurred during the first postoperative year. However, a smaller proportion of patients initiated therapy after 24 months, suggesting that continued monitoring may be appropriate among selected patients with higher preoperative thyroid-stimulating hormone levels, thyroid cancer, or persistently high-normal postoperative thyroid-stimulating hormone values.
The study had several limitations. The primary endpoint reflected treatment initiation rather than permanent thyroid hormone dependence. The investigators could not determine the specific indication for levothyroxine, particularly among patients with thyroid cancer, in whom therapy may have been initiated for thyroid-stimulating hormone management rather than replacement alone. In addition, they could not establish causality, and important clinical variables such as remnant thyroid volume and detailed tumor characteristics were unavailable.
The findings suggested that thyroid hormone therapy is common following hemithyroidectomy and that preoperative thyroid-stimulating hormone levels and thyroid cancer may help identify patients at greater risk of requiring postoperative treatment and monitoring.
“In conclusion, thyroid hormone therapy initiation after hemithyroidectomy is common in real-world practice, affecting 39.7% of [adults who] previously [had] euthyroid within 2 years and 46.3% over extended follow-up. Preoperative [thyroid-stimulating hormones] and thyroid cancer identify high treatment burden subgroups,” wrote lead study author Shmuel Wechsler, of the Department of Otolaryngology–Head and Neck Surgery at the Shamir Medical Center in Israel, and colleagues.
The study authors declared no conflicts of interest.
Source: Endocrine
