Decreasing incidence of thyrotoxicosis in an endemic goitre inland area of Sweden.

Four hundred and sixty-seven new cases of thyrotoxicosis were diagnosed during the period 1975-1984 in a demographically well defined Swedish inland county, with about 134,000 inhabitants, where goitre has been considered endemic. This corresponds to a mean annual incidence of all thyrotoxicosis of 34.7/100,000. The mean incidence of toxic diffuse goitre was 16.6/100,000 and of toxic nodular goitre 18.4/100,000. The mean incidence of all thyrotoxicosis fell from 39.2 to 30.2/100,000/year between the first and the second 5-year period of the study (P less than 0.01); this was entirely due to a decrease in the incidence of toxic nodular goitre (22.6 to 14.1/100,000/year) whereas the incidence of toxic diffuse goitre did not change significantly. The decrease in the incidence of toxic nodular goitre was evenly distributed over all age groups and over rural and urban areas of the county.