Psoriatic arthritis. Plain radiology and other imaging techniques

The incidence of radiological change in psoriatic arthritis (PsA) is uncertain. The general pattern of the disease has been classified into five groups. This classification is still widely used, but recently a change of emphasis has been stressed in the classification and prevalence, particularly relating to the polyarthritic forms and the variability of symmetry and asymmetry. The plain film findings in the axial and appendicular skeleton are described. In the former, bulky paramarginal ossification in the thoracolumbar spine is a prominent feature; destructive as well as ankylosing disease is seen in the cervical spine. In the latter, the key features are marginal erosions associated with proliferative new bone, acro-osteolysis, preservation of bone density, periostitis and bony ankylosis. Progress of the disease is variable and, while the course is usually less severe than that in rheumatoid arthritis, progressive joint deformity occurs. Isotope scintigraphy is a useful technique for showing a general overview of joint involvement, but has limitations which impair its use in individual joints. CT is useful for looking at detailed bone anatomy and early demonstration of sacroiliitis. MRI may also be used to look at early sacroiliitis and has the potential for directly imaging the inflammatory process and the articular cartilage. Radiological differentiation of PsA from other arthritides may be difficult, particularly in the early stages, and in oligoarticular disease. The differential diagnosis is discussed.