Abstract

The clinical appearance of psoriatic arthritis (PsA) is very diverse, involving the spine, sacroiliac joints, peripheral joints and/or entheses, and accordingly MRI findings vary. PsA shares clinical manifestations with rheumatoid arthritis and spondyloarthritis (SpA) and this also applies to its MRI features [1]. Peripheral PsA synovitis and erosions do not have disease-specific MRI features, and MRI bone edema can involve any bone. A general agreement on which joints to image to assess PsA activity and damage is not established, and possibly needs to be individualized, based on the disease pattern.

MRI can visualize both peripheral and axial musculoskeletal anatomy and PsA disease manifestations. Findings include synovitis, tenosynovitis, periarticular inflammation, enthesitis, bone edema, bone erosion and bone proliferation [2-5]. As in other types of SpA, enthesitis, dactylitis and spondylitis can be seen. Dactylitis has been shown on MRI to be due to tenosynovitis with effusion, sometimes associated with diffuse soft tissue edema and/or synovitis in nearby finger or toe joints [6,7]. There are few MRI studies in axial PsA, but findings are similar to findings in ankylosing spondylitis, although more frequently asymmetric [8,9].

The entheses has attracted attention, as a possible primary location of disease [10]. Nail disease is common in PsA, and DIP joint inflammation on MRI has been described to extend to the nail bed [11].

PsA can be clinically silent. In patients with psoriasis without arthritic signs or symptoms, pathological findings on MRI (including periarticular edema, tendon sheath effusion, intra-articular effusion, bone erosion, and joint subluxation) have been reported in >2/3 versus 0- 1/12 of healthy controls [12-14]. The clinical importance of these findings are not yet clarified.

As described above, MRI can detect the different pathologies involved in PsA. However, there are no studies that have documented that MRI in an early undifferentiated arthritis cohort can be used to differentiate PsA from other arthritides.

Data on the utility of MRI for monitoring activity and damage in PsA are limited. Most studies only report qualitative MRI assessments of the different pathologies of PsA [1]. Quantitative assessment of contrast enhancement has been reported [15,16], but is insufficiently validated for clinical use. Scoring systems of inflammation and damage has been developed [2,17,18], with the OMERACT Psoriatic Arthritis Magnetic Resonance Image Scoring System (PsAMRIS) [2,19] being the best validated, and with a documented good intra- and inter-reader reliability and, for inflammatory parameters (synovitis, tenosynovitis, periarticular inflammation), sensitivity to change. Its usefulness in clinical trials and practice needs further testing. No longitudinal studies of the prognostic value of MRI findings in PsA are available.

In summary, MRI is an excellent tool for evaluation of patients with PsA, because both peripheral and axial disease manifestations can be detected and monitored. However, despite encouraging data, further scientific work needs to be done before the value of different MRI techniques in diagnosis, monitoring and prognostication of PsA is clarified