Clinical and Epidemiological Studies on Giant Cell Arteritis

Objectives:
The aim of the research summarized in this thesis was to present a comprehensive view of the epidemiology of biopsy-confirmed GCA, investigate infection as a possible risk factor of GCA, and to assess the association of GCA with cancer and myocardial infarction.
Methods:
To establish incidence and prevalence, patients diagnosed with biopsy-confirmed GCA in Skåne, Sweden 1997–2019 were identified through the database of the pathology department of Region Skåne which serves the entire region. A non-GCA population matched with respect to age, sex, and place of residence was established for Studies II and III, using the Skåne Healthcare Register. The cohorts were cross-linked with several regional and national healthcare registers for the assessment risk factors and outcomes.
Results:
Study I revealed a decreasing trend in the incidence of biopsy-confirmed GCA over the more than two decades surveyed, with incidence decreasing by 2% per year. Forty-one percent of the identified patients were not receiving immunosuppressants at the point-prevalence date. Seasonal variation in incidence was evident, with more patients diagnosed in spring and summer, interesting in light of the findings of Study II, which showed infections to be associated with increased incidence of subsequent GCA diagnosis. Antecedent upper respiratory tract infections, influenza, and pneumonia were more common in patients with GCA compared to their referents. No increased risk for cancer overall was observed in Study III. However, compared with the general population, the observed incidence of myeloid leukaemia was higher in patients with GCA, while cancers of the breast and upper gastrointestinal tract were less frequent. The results of Study IV showed the incidence of MI to be higher in the first three months following GCA diagnosis and was associated with a 2.8-fold risk of death compared with GCA patients without MI.
Conclusions:
The decreased incidence of biopsy-confirmed GCA can likely be attributed to the expanding use of imaging for GCA diagnosis the increased awareness among clinicians of different GCA clinical phenotypes. A sizeable proportion of individuals with biopsy-confirmed GCA experience a favourable diseases course. Environmental exposures may play a role in triggering GCA in susceptible individuals. Elevated risk of MI and some cancers is seen after GCA diagnosis and intervention, probably related to systemic inflammation and steroid treatment. The lower risk for breast cancer and upper gastrointestinal tract cancer is a novel finding and needs to be confirmed by further research.