Endocrine Abstracts

Introduction: The incidence of hyperthyroidism is influenced by iodine nutrition. Sweden is a long-term iodine sufficient (IS) area with an iodination fortification program since 1936.

Methods: In 2003–2005, all referred cases of subclinical (SH) and overt hyperthyroidism (OH) were registered from a targeted population of 631239 individuals in Gothenburg. Information on age, gender, etiology, smoking, thyroid associated ophtalmopathy (TAO), thyroid hormone levels, TSH receptor antibodies (TRab), thyreoperoxidase antibodies (TPOab) and planned treatment was collected at diagnosis. Incidences were calculated. Comparisons between SH and OH for Graves’ disease (GD), toxic multinodular goiter (TMNG) and solitary toxic adenoma (STA) were made and for GD also smokers vs non-smokers, TRab⁺ vs TRab⁻, TAO⁺ vs TAO⁻, and correlations between thyroid hormone levels, age and autoantibodies.

Results: The total incidence of hyperthyroidism was 27.6/100000/year (OH 23.8/100000/year, SH 3.8/100000/year; GD 21.4/100000/year, TMNG 4.3/100000/year and STA 1.8/100000/year). SH was more common among TMNG and STA (40.2% and 45.7%)than in GD (15.1%). SH-GD patients were older, more often smokers and had lower TRab levels than patients with OH-GD. FT4 and T3 levels in GD were higher than in TMNG and STA. FT4, T3 and TRab decreased with age in GD patients (Spearman −0.23, −0.35, −0.26), P<0.0001. TRab⁻ patients had lower T3 than TRab⁺ patients (3.7±1.7 vs 5.7±2.8), P<0.001 but similar FT4 levels. TRab was positively correlated to FT4 (Spearman 0.39), P<0.0001. TAO occured in 20% of GD patients. TAO⁺ patients was younger than TAO⁻ patients. Concentration of FT4 and T3 were similar but TRab was higher in TAO⁺ patients. Smokers did not have more TAO.

Conclusion: The total incidence of hyperthyroidism was relatively low. The dominating cause was GD with an age-related decrease of thyroid hormones and TRab. The spectra of hyperthyroidism in this long-term IS area probably reflects the future for many countries with shorter history of IS.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.