Predictors of positive (18) F-FDG PET/CT-scan for large vessel vasculitis in patients with persistent polymyalgia rheumatica

Objective: Polymyalgia rheumatica (PMR) is often the presenting manifestation of giant cell arteritis (GCA). Fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) scan often discloses the presence of large vessel vasculitis (LVV) in PMR patients. We aimed to identify predictive factors of a positive PET/CT scan for LVV in patients classified as having isolated PMR according to well-established criteria. Methods: A set of consecutive patients with PMR from a single hospital were assessed. All of them underwent PET/CT scan between January 2010 and February 2018 based on clinical considerations. Patients with PMR associated to other diseases, including those with cranial features of GCA, were excluded. The remaining patients were categorized in classic PMR (if fulfilled the 2012 EULAR/ACR classification criteria at disease diagnosis; n=84) or atypical PMR (who did not fulfill these criteria; n=16). Only information on patients with classic PMR was assessed. Results: The mean age of the 84 patients (51 women) with classic PMR was 71.4±9.2 years. A PET/CT scan was positive in 51(60.7%). Persistence of classic PMR symptoms was the most common reason to perform a PET/CT scan. Nevertheless, patients with positive PET/CT scan often had unusual symptoms. The best set of predictors of a positive PET/CT scan were bilateral diffuse lower limb pain (OR=8.8, 95% CI 1.7-46.3; p=0.01), pelvic girdle pain (OR=4.9, 95% CI 1.50-16.53; p=0.01) and inflammatory low back pain (OR=4.7, 95% CI 1.03-21.5; p=0.04). Conclusion: Inflammatory low back pain, pelvic girdle and diffuse lower limb pain are predictors of positive PET/CT scan for LVV in PMR