About 90% of all functional thyroid autonomies (FTA) are euthyroid for a prolonged period of time. It is estimated that more than 10% of goiter patients in iodine deficient regions and less than 10% in iodine rich areas have evidence of FTA. After the age of 40, the risk of hyperthyroidism decompensation gradually increases. This risk rises with increasing thyroid volume, nodularity and patient age. In the elderly, hyperthyroidism also occurs in the absence of goiter. After decades of iodine deficiency, especially the intake of unphysiologically high iodine concentrations may result in increased frequencies of hyperthyroidism. In iodine deficient regions, almost half of all cases of hyperthyroidism are FTA related. Following elimination of iodine deficiency, the rate of hyperthyroidism may be reduced below 10%. This will not affect the prevalence of immunogenic hyperthyroidism. The most reliable evidence of FTA is produced using the TcTU supp. test. The highly sensitive TSH0 and the TRH test are 2.5 times less sensitive. Thus, they may still indicate euthyroidism in scintigraphically compensated or decompensated FTA. The TSH0 screening is only recommended with a view to an improved cost/benefit ratio in the elderly, females above the age of 40, and ill persons. Acutely ill and psychiatric patients should be excluded. Already 1 year after the introduction of iodine into the medical treatment of thyroid disorders, Coindet reported in 1821 his epidemiologically relevant clinical observation of an increase in hyperthyroidism, predominantly of the functional autonomy type. In the meantime, detailed and universally accepted knowledge has become available on the pathogenesis and pathophysiology of functional thyroid autonomy (Gerber et al., 1985). Data on the epidemiology of functional autonomy continue to apply only to the regional population they are based on. They allow to draw conclusions on the prevalence and natural course of functional thyroid autonomy (FTA). The different forms and prevalence rates of hyperthyroidism reflect the severity and duration of the nutritional iodine deficiency on one hand and the quality of iodine prophylaxis on the other.
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