Large vessel vasculitis (LVV) causes blood vessel inflammation leading to pain, fatigue and complications such as aneurysm formation and stroke. Treatments used can have significant side-effects. Doctors find it difficult to determine when to start and stop treatment, often leading to over- or under-treatment. A new test is required to determine disease activity that will guide treatment more accurately. This study will recruit participants with active LVV from throughout Scotland in order to assess the ability of two new types of scan - positron emission tomography with magnetic resonance imaging (PET/MR) and retinal optical coherence tomography (OCT) - to determine disease activity. In addition, I will investigate the link between LVV and heart disease.

Large vessel vasculitis (LVV) is a multi-system, autoimmune disease characterised by non-specific symptoms, pain and high glucocorticoid requirements. The lack of a robust biomarker that tracks disease activity makes disease monitoring difficult. This leads to both disease over-treatment, resulting in adverse effects of glucocorticoids, and under-treatment, with the potential for significant vascular complications. Additionally, the link between LVV and cardiovascular disease (CVD), which is the main cause of death in these patients, remains poorly characterised. An imaging tool which is capable of accurately monitoring disease activity over time is urgently required. Positron emission tomography with magnetic resonance imaging (PET/MR) and retinal optical coherence tomography (OCT) have the potential to meet this need. PET/MR is uniquely useful for imaging CVD and utilises ~50% of the radiation dose of PET with computerised tomography. OCT is a novel potential biomarker of microvascular dysfunction, systemic inflammation and CVD risk in small vessel vasculitis. Participants with a new diagnosis or recent flare of LVV will undergo serial PET/MR and OCT scanning alongside established measures of CVD risk. Results will be compared with current clinical measures of disease activity and with banked control data.

Inclusion Criteria:

• A new diagnosis of LVV or a known diagnosis of LVV presenting with disease relapse

Exclusion Criteria:

• Predominantly cranial symptoms
• LVV secondary to other conditions
• Treatment with high dose glucocorticoids for >2 weeks at time of recruitment
• Contraindication to MR or PET
• Unable to travel to Edinburgh
• Estimated glomerular filtration rate (eGFR) <30 ml/min/1.73m2
• Unable to provide informed consent
• Pregnant or breastfeeding

Participants will be recruited from outpatient clinics throughout Scotland