Plain radiography

Psoriatic arthritis is a destructive inflammatory arthritis that can affect the peripheral and axial skeleton of patients with psoriasis. Plain radiography has formed an important part in defining psoriatic arthritis as a distinct clinical entity, from early work reporting on distinguishing features to more recent inclusion of osteoproliferation in the CASPAR classification criteria. Plain radiography is accessible, inexpensive and remains the standard measure of assessing damage in inflammatory arthritis. Originally considered a benign disease psoriatic arthritis is now recognised to be destructive and progressive, though not as aggressive as rheumatoid arthritis. Peripheral joint damage is characterised by erosions, joint space narrowing, osteoproliferation, osteolysis and ankylosis. Approximately twenty percent of patients have erosive disease at diagnosis progressing to approximately half of all patients by three years disease duration. In its most severe form, psoriatic arthritis mutilans, digits become shortened from gross bone resorption (osteolyisis) leading to severe functional impairment and disability. Spondyloarthritis may affect between 25-70% of patients with PsA. The radiographic features of Psoriatic Spondyloarthritis differ from Ankylosing Spondylitis, in that sacroiliitis is often asymmetrical and less severe, the cervical spine is frequently involved and syndesmophytes are asymmetrical and para-marginal. Overall radiographic features are less severe than ankylosing spondylitis. The natural history of both peripheral and axial radiographic damage in psoriatic arthritis in the modern era of early diagnosis, tight disease control and biologic drugs has yet to be established.