Development of hypothyroidism following hemithyroidectomy: A population-based study.

[PURPOSE] Hypothyroidism is a known possibility after hemithyroidectomy, with a highly variable incidence in the literature ranging from 8 to 60 %. Incidence of hypothyroidism after hemithyroidectomy was evaluated with a secondary aim to assess incidence in patients with Hashimoto's disease.

[MATERIALS & METHODS] A retrospective study using the TriNetX global federated research network was performed. We included patients within the last 15 years that were ≥18 years of age and had Current Procedural Terminology codes for hemithyroidectomy. Patients were excluded if they had a total or completion thyroidectomy at any time, a history of thyroid cancer, were preoperatively either on levothyroxine, diagnosed with hypothyroidism, or had a Thyroid Stimulating Hormone ≥ 4 m[IU]/L. We assessed the 3 month incidence of hypothyroidism postoperatively based on the International Classification of Diseases code, TSH ≥ 4 m[IU]/L, or taking levothyroxine after surgery.

[RESULTS] 6845 patients met the inclusion criteria. Most of the cohort was female (67 %) and white (63 %). The mean age at surgery for this population was 54 ± 14.8 years. During the 15 years of data, we found the 3-month incidence of hypothyroidism following hemithyroidectomy to be 23.58 %. The median time to develop the disease was 41.8 months. A subgroup analysis of those with Hashimoto's revealed a 3-month incidence of 31.1 % of patients developing hypothyroidism after surgery.

[CONCLUSIONS] This population-based study gives additional insight into the incidence of hypothyroidism after hemithyroidectomy. This will help improve perioperative patient counseling and management.