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

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 99ᵐTc 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.