Epidemiology of thyroid diseases in iodine sufficiency

Epidemiology of thyroid diseases in iodine-sufficient areas (ISA) deals wit h sporadic goiter, thyroid autoimmune diseases, and thyroid cancer. A compa rison between the different studies performed is difficult because methods have changed over time and selection criteria and definitions such as preva lence or incidence were not used consistently by some authors. Sporadic goi ter: in ISA, autoimmune processes play a major role in the development of s poradic goiter. In adults, sporadic diffuse goiter is most frequent in youn g women (16%), perhaps due to additional relative iodine deficiency especia lly in pregnancy, and declines with age (<10%). Sporadic nodular goiter inc reases from 5% in young women to 9% in older women. Autoimmune thyroid dise ase (AITD): thyroid autoantibodies (TAb) and histopathological lymphocytic infiltration of the thyroid is much more common in ISA (4.6% in women; 1.1% in men) than in iodine-deficient areas (IDA). The prevalence and incidence of hypothyroidism and hyperthyroidism varies, depending on whether overt a nd subclinical forms are included and whether newly or previously diagnosed dysfunction is considered. In an overview of the literature, the prevalenc e is 2 in 1000 for overt and 6 in 1000 for subclinical hyperthyroidism in I SA. The values for hypothyroidism are 5 in 1000 and 15 in 1000, respectivel y. Change from IDA to ISA: in former IDA, the percentage of hyperthyroidism increases up to 4 years after salt iodination. Whereas this effect is tran sient for Plummer's disease, a change from IDA to ISA seems to lead to a pe rmanent increase in overt and subclinical Graves' disease. Thyroid cancer: most studies demonstrate that the histopathological types of thyroid cancer are different in IDA and ISA. There is a tendency toward an increase in di fferentiated and decrease of anaplastic cancer. The ratio of papillary to f ollicular thyroid cancer ranges from 6.5:1 to 3.4:1 in areas with high iodi ne intake, decreases 3.7:1 to 1.6:1 in areas with moderate iodine intake, a nd ranges from 1.7:1 to 0.19:1 in IDA.