Clinical and Immunogenetic Characterization of Giant Cell Arteritis (GCA) and Polymyalgia Rheumatica (PMR)

Giant cell arteritis (GCA), also known as temporal arteritis, is the most common form of primary systemic vasculitis, with up to 75,000 cases a year identified in the EU and US. It occurs almost exclusively in people over the age of 50 years and is considered to be a medical emergency. If not treated with high-dose glucocorticoids immediately, the thickening of the inflamed blood vessel wall can cause irreversible visual loss or stroke. GCA can lead to significant morbidity across a variety of systems, due to both the disease, and complications of treatment. Diagnosis may be confirmed with a temporal artery biopsy, imaging (e.g. USS/CT/MRA/PET-CR) or based on clinical signs (e.g. erythrocyte sedimentation rate) and symptoms (e.g. a new headache, jaw claudication, visual disturbances, temporal artery abnormality such as tenderness or decreased pulsation) .

Polymyalgia rheumatica (PMR) is characterised by inflammatory limb-girdle pain with early morning stiffness, and a systemic inflammatory response demonstrated by elevated inflammatory markers.

The UK GCA Consortium is a multi-centre observational study, the main arms of which recruit prospective (participants with suspected GCA) and retrospective cohorts (participants with confirmed GCA diagnosis). Analysis of data collected on these cohorts will help achieve the primary aim of finding genetic determinants of GCA and PMR susceptibility, in order to yield novel insights into disease pathogenesis. Secondary aims, and their associated analyses, are as follows:

• Phenotype: characterising GCA and PMR subtypes, based on clinical features; imaging; cells; subcellular fractions and molecules in the circulation and/or arterial tissue; genetic/epigenetic/transcriptomic/proteomic or metabolomics factors, including next generation sequencing (whole exome sequencing) of selected cases.

• Life impact: determining what aspects of the disease and treatments affect patients' quality of life, as assessed by patient-reported outcomes.

• Long-term outcomes: characterising prognosis of GCA and PMR - both effects of the disease and its treatment - by longitudinal follow-up through electronic linkage to health records.

• Exploratory analyses: exploring the potential role of environmental factors and co-morbidities on phenotype and outcomes.

• Diagnosis, prognosis: improving diagnosis of GCA and PMR, and identifying factors that predict diagnosis, such as diagnostic clinical features, and prognostic and diagnostic biomarkers.

• Disease activity: monitoring participants who commence a synthetic or biological disease-modifying anti-rheumatic drug (s/bDMARD). Finding a biomarker for GCA and PMR disease activity, which might be clinically useful in helping to optimise steroid and s/bDMARD treatments for individual patients.