MRI and ultrasonography for diagnosis and monitoring of psoriatic arthritis.

Imaging techniques such as magnetic resonance imaging (MRI) and ultrasound (US) have been increasingly used in psoriatic arthritis (PsA) providing additional clues to the pathogenesis of this peripheral, axial and dermatologic disease. This has improved our understanding of the disease and can be used to aid diagnosis and then to follow outcomes of treatment. Both imaging modalities have highlighted the differing involvement of PsA when compared with rheumatoid arthritis (RA) with a significant burden of entheseal disease, flexor tenosynovitis (occurring alone or as part of dactylitis) and other extra-capsular inflammatory changes. MRI scanning has also highlighted the link between the nail and the distal interphalangeal (DIP) joint confirming previous clinical observations. Imaging studies in psoriasis patients have discovered a high level of subclinical inflammatory change but the clinical importance of such findings has not yet been defined. The potential use of MRI and US to monitor treatment outcomes has encouraged research in this field. In MRI, the PsA MRI Score (PsAMRIS) has been developed with promising initial validation. In US, work is ongoing with the OMERACT group to define key pathologies and to develop scoring systems. A few scoring systems are available for enthesitis scoring using US which are further being developed and refined. Further improvements in technologies in both of these fields offer exciting possibilities for future research. New MRI techniques offer the chance to image previously 'dark' structures such as tendons which is key in spondyloarthritides (SpA). Sonoelastography may also improve our understanding of tendon involvement in SpA. Whole-body multi-joint MRI allows a 'snapshot' of inflammation in PsA including joints, entheses and spinal involvement. Three-dimensional US should improve reliability and comparability of US scoring reducing inter-operator variability. The latest machines offer real-time fusion imaging employing US machines with an in-built virtual navigator system linked to previous MRI acquisitions. All of these new techniques should aid our understanding of PsA and our ability to objectively measure response to therapy.