49. Seasonal Variation in GCA

Background: Giant Cell Arteritis (GCA) is the most common primary systemic vasculitis in adults, occurring in individuals over age 50, most frequently in women (3:1, F:M) and in those of Northern European descent. While genetic factors likely contribute to the increased incidence in Northern Europe, environmental triggers are also likely to play a role. Cyclical and seasonal fluctuations in incidence have been demonstrated in some cohorts. It is plausible that environmental triggers may play a role in inducing vascular inflammation but may also contribute to the differing patterns of disease seen in GCA. Aim: The objective of this study is to investigate the seasonal variation in the incidence of GCA. Methods: This study used data from the St Vincent’s University Hospital GCA registry of 340 patients who were prospectively recruited from three hospital sites, in Dublin, over a 7-year period. We looked at month and year of onset of GCA symptoms and the variation in clinical phenotype at diagnosis, investigating for trends based on season of diagnosis. Results: We had complete data for 5 years: 2012-2016 inclusive. Over these 5 years, 306 patients were diagnosed with GCA, 65% females and 35% males with a mean age of 71. Based on the date of onset of symptoms, we found an overall peak in the incidence of GCA in late spring / early summer and another smaller peak in late autumn / early winter. 64% presented with uncomplicated cranial GCA, 22% of patients had an ischaemic complication at diagnosis, 11% of patients presented with PMR with subclinical vasculitis and 3% with only constitutional symptoms. We did not observe any seasonal variation in these phenotypes. Conclusion: We found a seasonal variation in the incidence of GCA with peaks in the late spring / early summer and late autumn / early winter. Following on from this study, by using data from the international TABUL and DC VAS datasets, we aim to investigate further the seasonal, cyclical and geographical variation in incidence in GCA. Disclosures: Non