Prevalence and characteristics of subclinical polymyalgia rheumatica in patients with giant cell arteritis

To determine the prevalence, characteristics and clinical significance of subclinical polymyalgia rheumatica (PMR) in patients with apparently isolated giant cell arteritis (GCA).

Single-centre retrospective cohort study including 168 patients with newly diagnosed GCA who underwent 18F-FDG PET-CT (18F-fluorodeoxyglucose positron emission tomography-computed tomography) at diagnosis. Patients were classified into clinical PMR, subclinical PMR or pure GCA based on PET findings and clinical symptoms. FDG uptake was assessed at predefined typical PMR sites, and only sites with grade ≥2 uptake were considered positive. Subclinical PMR was defined as FDG uptake involving either bilateral periarticular shoulders or bilateral trochanteric bursae or ischial regions, plus uptake at one additional typical PMR site.

PET findings consistent with subclinical PMR were observed in 56% (57/102) of patients with apparently isolated GCA at diagnosis. A substantial proportion of these patients fulfilled different proposed PET-based diagnostic criteria for PMR. Patients with GCA and subclinical PMR showed less extensive musculoskeletal FDG uptake than those with GCA and clinical PMR but greater large-vessel involvement than pure GCA, particularly in the thoracic aorta (P = 0.023), abdominal aorta (P = 0.0001) and supra-aortic trunks (P = 0.007). Compared with pure PMR, they displayed a milder and more localized inflammatory pattern, mainly affecting the shoulder and pelvic girdles. No significant differences were observed across groups in cranial manifestations, severe ischaemic events, systemic inflammation or relapse rates.

Subclinical PMR findings are frequently detected by PET-CT in patients with apparently isolated GCA, supporting the concept of a GCA-PMR spectrum disease.