Serum thyroid autoantibodies as a risk factor for development of hypopthyroidism after radioactive iodine therapy for single thyroid 'hot' nodule

Abstract

Abstract. Hypothyroidism is often observed after radioiodine treatment in Graves' disease, but it is considered a rare complication in single hyperfunctioning thyroid nodule ('hot' nodule). This concept has been recently challenged, but the available data are conflicting. In the present study we therefore assessed the development of permanent hypothyroidism in 126 patients with thyroid hot nodule treated with 131I (180 μCi/g of estimated nodule weight, total dose 5.5–28.9 mCi). Follow-up ranged between 1 to 11 years. Hypothyroidism was observed in 5 (4%) patients, corresponding to a cumulative incidence by life-table analysis of 4.8% ten years after treatment. No relationship was found between the development of hypothyroidism and the size of the nodule or the total amount of administered dose. Fifty-six patients with euthyroid hot nodule at the time of treatment had higher cumulative incidence of hypothyroidism after 10 years (9.7%) than those with toxic adenoma (1.5%) (0.1 > P > 0.05 by logrank test). When the patients were analyzed according to the presence or absence of serum antithyroglobulin and/or antithyroid microsomal autoantibodies, the prevalence of hypothyroidism after 131I treatment was higher (4/25 = 16%) in patients with significant serum antibody titres (≥ 1/400 by pasive haemagglutination), when compared to that observed in subjects with negative antibody tests (1/101 = 1.0%). Life-table analysis showed in antibody positive patients a cumulative incidence of hypothyroidism after 10 years of 18.0% vs 1.4% in antibody negative patients (P <0.001 by log-rank test). In conclusion, the present data provide the first evidence that coexistent thyroid autoimmunity is a significant risk factor for the development of hypothyroidism in patients with hot nodule treated with radioiodine.