Hemithyroidectomy Is Associated With a Lower Rate of Hypothyroidism Than Radioactive Iodine Therapy for Solitary Toxic Nodules

ABSTRACT Background For solitary toxic adenoma (STA) hemithyroidectomy and radioactive iodine (RAI) both cure hyperthyroidism, but their hypothyroidism risks differ. Aim To review the thyroid status of patients who had received definitive therapy for a STA to determine differences in the hypothyroidism rates between those who underwent surgery as compared with RAI. Methods Retrospectively collected cohort study (2010–2020) from a single centre in New Zealand. STA was defined by a low TSH and solitary hot nodule on 99 ᵐTc imaging. Primary outcome was hypothyroidism at 12 months. Results Among 98 patients (RAI 48; surgery 50), cure of hyperthyroidism was 98% (RAI) versus 100% (surgery). After excluding those with missing data, hypothyroidism at 12 months occurred in 12/44 (27%) after RAI versus 3/45 (6.7%) after surgery (absolute risk difference ~20%; NNT≈5). Of those with biochemical hypothyroidism, 9/12 RAI patients were treated with levothyroxine and 2/3 in the surgical group. In multivariable analysis, RAI was associated with higher odds of hypothyroidism versus surgery. Conclusion Both treatments are effective, but when using a fixed dose 555 MBq RAI protocol, hemithyroidectomy is associated with substantially lower hypothyroidism risk. Findings support shared decision‐making that weighs patient preference to avoid lifelong levothyroxine against operative risks and local expertise.