Increased annual frequency of Hashimoto's thyroiditis between years 1988 and 2007 at a cytological unit of Sicily.

Like other auto-immune diseases, Hashimoto's thyroiditis (HT) results from the interaction of genetic with environmental factors. Only few studies have evaluated the year-to-year change in frequency of HT over a wide period of time. The endocrine division of our Hospital has reported a great increase in the annual frequency of HT between 1975 and 2005, and a progressive decrease in both age at presentation and female to male (F/M) ratio starting in the mid-1990s. Between years 1988 and 2007, we have collected 8397 adequate examinations by fine needle aspiration cytology (FNAC) on 8397 persons referred for the evaluation of a solitary or dominant thyroid nodule (total FNAC and persons=8520) with a 14-fold increase in 2007 over 1988. In this 20-year period, cases of HT, De Quervain's thyroiditis (DQT) and Riedel's thyroiditis (RT) were 490, 36 and two, respectively. HT cases were one in 1988 but 90 in 2007, with a significant upward temporal trend (r=0.919, P<0.001) and significant downward trend for age at FNAC (r=-0.466, P<0.05). In contrast, DQT cases were zero and one, respectively, with no significant temporal trend (r=0.29, P=0.21). The HT increase in frequency started in 1996 (+350% over 1995). Until 1995 there was only one man, but there were 22 men in 2005-2007. These FNAC data provide independent confirmation to the data from the endocrine division of the same hospital, further supporting the conclusion that only environmental modifications can explain these marked changes that have occurred in such a relatively short period of time.