Incidence rate and clinical features of hyperthyroidism in a long-term iodine sufficient area of Sweden (Gothenburg) 2003-2005

SummaryObjectives To study hyperthyroidism in long-term iodine sufficiency (IS), as iodine supply affects its occurrence. Design Prospective descriptive study. Patients In 2003–2005, all referred cases of subclinical (SH) and overt hyperthyroidism (OH) were registered at diagnosis from a population (n = 631 239) in Gothenburg, Sweden. Measurements Information on age, gender, smoking, thyroid associated ophthalmopathy (TAO), thyroid hormones and TSH receptor antibodies (TRab) was collected. Incidences were calculated. SH and OH cases with Graves' disease (GD), toxic multinodular goiter (TMNG) and solitary toxic adenoma (STA) were compared. In GD, TRab+ and TRab− cases and patients with (TAO+) and without TAO (TAO−) were compared. Results The total incidence (n/100 000/year) of hyperthyroidism was 27·6; OH 23·8; SH 3·8; GD 21·4; TMNG 4·3; and STA 1·8. SH was more common among TMNG (40·2%) and STA (45·7%) than in GD (5·9%). SH-GD patients were older, more often smokers and had lower TRab levels than OH-GD patients. FreeT4 and T3 levels in GD were higher than in TMNG and STA. FreeT4, T3 and TRab decreased with age in patients with GD, P