The distinct phenotype of subclinical giant cell arteritis in polymyalgia rheumatica: evidence from a PMR fast-track clinic.

Objectives: To define the prevalence and phenotype of subclinical giant cell arteritis (sGCA) in newly diagnosed polymyalgia rheumatica (PMR). Methods: This prospective study assessed consecutive patients referred from primary care to a fast-track clinic (FTC) with suspected PMR without GCA features. Patients were compared with a control population which consisted of newly diagnosed, consecutive patients with GCA from an FTC. Assessment included temporal and axillary artery ultrasound and quantitative scoring using Halo count (HC), Halo score (HS), and OMERACT GCA Ultrasound Score (OGUS). Patients with PMR with positive vascular ultrasound findings were diagnosed as sGCA. Cardiovascular risk (American College of Cardiology/American Heart Association Atherosclerotic Cardiovascular disease [ASCVD] score) was calculated. Results: Seventy-three new PMR and 24 new patients with GCA were included. Twenty-five percent of patients with PMR had ultrasound-confirmed sGCA. Although predominantly male (80% vs 45%), sGCA could not be otherwise clinically differentiated. PMR with sGCA had more extracranial involvement than GCA (47% vs 33%) with lower baseline OGUS scores (0.81 [±0.17] vs 0.96 [±0.21], Conclusions: This study found that 1 in 5 patients with PMR referred from primary care via an FTC have sGCA. sGCA has a distinct ultrasound phenotype from GCA, with lower vessel wall inflammation quantified by the OGUS, than observed in GCA. A higher clinical and ultrasound relapse rate in patients with sGCA may support closer monitoring and intensive treatment of these patients.