Imaging of psoriatic arthritis

Imaging of psoriatic arthritis (PsA) is important for two reasons: the differential diagnosis from other arthritides and the assessment of structural damage that can be inhibited by the new drugs such as the anti-TNFalpha agents. Plain film radiographic findings of peripheral arthritis have been important in elaborating the concept of PsA as a separate disease entity. Characteristic aspects of psoriatic peripheral arthritis help the differentiation from rheumatoid arthritis. High-resolution ultrasonography (US), US combined with power Doppler (PDUS) and magnetic resonance imaging (MRI) can be used to image joint synovitis of PsA. Radiologic features of spondylitis associated with psoriasis are similar to spondylitis associated with reactive arthritis and differ from those of primary ankylosing spondylitis (AS) and the spondylitis associated with inflammatory bowel disease. MRI is very sensitive for the early diagnosis of sacroiliitis. There have been no MRI studies on the spine of patients with PsA. In primary AS bone oedema in the vertebral bodies is an indicator of active disease and can ameliorate during anti-TNFalpha therapy. Historically, plain film radiography have played a pivotal role in defining enthesitis lesions of SpA. However, entheseal bone changes appear late. US and MRI have proved to be a highly sensitive and non invasive tools. Recent US and MRI studies on both finger and toe dactylitis have established that dactylitis is due to flexor tenosynovitis and marked adjacent soft tissue swelling with a variable degree of small joint synovitis. There is no evidence of enthesitis of the insertion of the flexor digitorum tendons and of the attachment of the capsule of the digit joints.