Imaging indications in polymyalgia rheumatica

The diagnosis of polymyalgia rheumatica (PMR), characterized by proximal pain and stiffness, is often uncertain owing to PMR mimics, such as rheumatoid arthritis (RA), spondyloarthritides, inf lammatory myopathies connective tissue diseases and vasculitis – all of which can present with the polymyalgic syndrome in the elderly. Inflammatory markers are often discordant with disease activity and imaging techniques show promise in diagnosis and disease monitoring, improving our understanding of PMR and its overlap with inflammatory arthritis and large vessel vasculitis (LVV). In this article, we discuss imaging techniques, primarily ultrasonography (US), but also MRI and f ludeoxyglucose (FDG)-PET, in the assessment of PMR. Current guidelines recommend a stepwise approach to PMR and we add the imaging requirements to facilitate the various diagnostic steps (Figure 1). Imaging adds to PMR diagnosis by either identifying abnormalities associated with alternative diagnoses or detecting PMR-specific features. MRI studies have shown synovitis and periarticular inflammation in PMR and confirm that there is no actual muscle inflammation [1], while FDG-PET scans show vascular inflammation, synovitis, bursitis and enthesitis in a significant portion of PMR patients [1]. Recently published PMR classification criteria recognize PMR-associated ultrasound lesions in the shoulders and hips as criteria items for the scoring algorithm for the classification as PMR [2]. We review the current understanding of the role of ultrasound, MRI and PET-CT and imaging in the diagnosis of PMR and distinguishing it from its mimics. In light of the classification criteria, we also report validation findings from a shoulder ultrasound study of consecutive patients referred from general practice for evaluation of suspected PMR. Synovitis, effusion, tenosynovitis and erosions referred in this paper are defined according to the Outcome Measures in Rheumatology (OMERACT) definitions for musculoskeletal (MSK) ultrasound [3].