MRI in psoriatic arthritis: insights into pathogenesis and treatment response.

Psoriatic arthritis (PsA) is a clinically heterogeneous condition, and not surprisingly, its MRI features are diverse. Synovitis and accompanying synovial effusions are clearly depicted, and enthesitis is characterized by extracapsular inflammation at the insertions of ligaments and tendons plus accompanying bone edema at bony attachments. Other forms of MRI bone edema include subchondral and diaphyseal involvement; the latter seeming relatively specific to PsA. The pathology of dactylitis can also be elucidated by MRI, which frequently reveals tenosynovitis and soft tissue edema in conjunction with various degrees of synovitis, bone edema, and erosion. Bone erosions differ from those seen in rheumatoid arthritis in their distribution and associated features such as bone proliferation and sometimes periostitis. Finally, MRI can be used to score and quantify these pathologic features, providing a sensitive tool with which to evaluate disease progression.