Low incidence of late-onset giant cell arteritis during the first year in patients with polymyalgia rheumatica–a repeated imaging study

The objective was to investigate the incidence of late-onset giant cell arteritis (GCA) within the first year in patients diagnosed with polymyalgia rheumatica (PMR). In this prospective study, treatment-naïve individuals with a new clinical diagnosis of PMR and without GCA symptoms underwent baseline assessments, including vascular ultrasonography and 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography computed tomography (FDG-PET/CT). To prevent biased inclusion, rapid referral clinics were established for all patients suspected of PMR. Additionally, the patients underwent GCA monitoring during clinical visits at weeks 8 and 10, which involved vascular ultrasonography and FDG-PET/CT scans. After one year, a follow-up visit was performed to confirm the PMR diagnosis and perform vascular ultrasonography. A final PMR diagnosis was assigned to 62 patients, excluding two patients with concurrent subclinical GCA and PMR at baseline, corresponding to a baseline prevalence of subclinical GCA of 3%. During the one-year follow-up, two PMR patients developed late-onset GCA corresponding to an incidence rate of 32 per 1000 person-years. One patient developed GCA 14 weeks after the PMR diagnosis, exhibiting cranial symptoms and positive vascular ultrasonography. The other patient presented with subclinical large vessel GCA at the one-year visit detected with vascular ultrasonography and confirmed by FDG-PET/CT. This study is the first to demonstrate a low incidence rate of late-onset GCA in PMR patients within the first year, employing repeated imaging to exclude GCA at baseline and diagnose GCA during follow-up. Additionally, it provides evidence of a low prevalence of subclinical GCA across the entire PMR population. ClinicalTrials.Gov, NCT04519580.