Prevalence, characteristics, and outcome of subclinical vasculitis in polymyalgia rheumatica: a retrospective cohort study

Objectives: Two recent meta-analyses reported subclinical vasculitis in 22-23% of patients with PMR. We aimed to evaluate the prevalence, characteristics, and outcome of subclinical vasculitis among our PMR patients. Methods: Consecutive patients with GCA/PMR spectrum disease with isolated PMR symptoms who underwent FDG PET imaging between 2003 and 2020 and who were followed for >= 6 months, were included retrospectively. Vasculitis was defined as FDG uptake >= grade 2 in any vessel. Results: We included 337 patients, of whom 31 (9%) with subclinical vasculitis. Among those with subclinical vasculitis, 21 (58%) had isolated large vessel vasculitis, 3 (10%) had isolated cranial vasculitis and 7 (23%) had both cranial and large vessel vasculitis. The glucocorticoid (GC) starting dose and GC doses during follow-up were higher in those with subclinical vasculitis until 12 months after diagnosis (P < 0.001). There was no difference in the duration of GC treatment (25 vs 20 months, P = 0.187). Cox proportional hazard regression analyses showed no difference in the proportion of patients able to stop GC (HR 0.78 [95% CI 0.49-1.25], P = 0.303) and in the proportion of patients with relapse (HR 0.82 [95%CI 0.50-1.36], P = 0.441). Conclusion: Only 9% of our PMR patients had subclinical vasculitis with a predilection for large vessel vasculitis. There were no differences in relapse rate and duration of GC treatment, however, those with subclinical vasculitis received higher GC doses until 12 months after diagnosis. Prospective interventional trials are needed to evaluate the outcome of PMR patients with and without subclinical vasculitis treated with a similar GC protocol.