A seasonal occurrence of Graves disease (GD) has been reported in previous studies, with a peak of frequency in the warmer half of the year (Ford 1988, 1991, Westphal 1994) or the period of the year with a higher iodine intake (Phillips 1985); other studies (Facciani 2000) have failed to find a different seasonal occurrence of Graves orbitopathy (GO). Aim of the present study was to evaluate a possible seasonal difference in the onset of GD and GO in a series of outpatient followed in our Department from April 2002 to October 2008.
About 551 patients with GD and GO were studied retrospectively by analyzing our database. Patients were seen in 1500 consecutive ophthalmological examinations. The mean (±S.E.M.) age at diagnosis was 44.2±0.6 years. Mean (±S.E.M.) time interval between the diagnosis of GO and GD and the onset of symptoms was 5.32±0.5 and 4.61±0.3 months, respectively. We found an increased prevalence of the diagnosis of GO in May (P< 0.03) and from August to September (P<0.004 and 0.045) compared to the rest of the year. Similarly, a diagnosis of GD was more frequent in the months of July, August and September (P<0.032, 0.014 and 0.005, respectively). In conclusion, our study shows that although both GD and GO are more frequently occurring during the warmer periods of the years, in accordance to previous studies, GO has a characteristic peak of frequency also in the month of May. These findings suggest perhaps some environmental factors may act as initial triggers of thyroid autoimmunity, similarly to what reported in other autoimmune disease such as type 1 diabetes.