Hyperthyroidism incidence in a large population-based study in northeastern Italy

Objective: an improvement in iodine status in Veneto region has been documented in the last decade. We aimed at estimating the incidence of hyperthyroidism in the Veneto region (Italy) over the period 2013-2022. Methods: retrospective population-based study conducted in Veneto (4.9 million people) using the population registry, an administrative health database. Between 2012 and 2022, hyperthyroidism incidence was defined thank to a healthcare co-payment exemption for hyperthyroidism or any hospital diagnosis of hyperthyroidism. Incident hyperthyroidism was defined from 2013 to 2022 to exclude prevalent cases. Standardized incidence rates (IR) were reported by age, sex and etiology of thyroid hyperfunction too. Results: we identified 26,602 incident cases (IR of 54.38 per 100,000 person-years, 2.47-fold higher in females than in males). IR decreased from 69.87 (95%CI, 67.49, 72.25) in 2013 to 42.83 (95%CI, 40.99, 44.66) in 2022. In 2020, an out-of-trend decrease in hyperthyroidism incidence was documented, corresponding to the SARS-CoV-2 pandemic outbreak, with a realignment to the trend in the subsequent years. The annual percentage change according to the cause of hyperthyroidism was as follows: -6.62% (95%CI, 8.47, 4.73) (P<0.0001) in toxic multinodular goiter, -7.56% in toxic uninodular goiter (95%CI, 10.54, 4.48) (P<0.001) and -4.70% (95%CI, 6.33, 3.04) in toxic diffuse goiter (Graves' disease) (P<0.001). Conclusions: we documented a decline in the incidence of hyperthyroidism in the Veneto region, paralleling the improvement of the iodine status, thanks to a long and sustained iodine prophylaxis campaign. SARS-CoV-2 pandemic and vaccination campaign did not change the declining trend of hyperthyroidism incidence in our region.