Psoriatic arthritis.

Psoriatic arthritis (PsA) is a chronic inflammatory joint disease which develops in patients with psoriasis. It is characteristic that the rheumatoid factor in serum is absent. Etiology of the disease is still unclear but a number of genetic associations have been identified. Inheritance of the disease is multilevel and the role of environmental factors is emphasized. Immunology of PsA is also complex. Inflammation is caused by immunological reactions leading to release of kinins. Destructive changes in bones usually appear after a few months from the onset of clinical symptoms. Typically PsA involves joints of the axial skeleton with an asymmetrical pattern. The spectrum of symptoms include inflammatory changes in attachments of articular capsules, tendons, and ligaments to bone surface. The disease can have divers clinical course but usually manifests as oligoarthritis. Imaging plays an important role in the diagnosis of PsA. Classical radiography has been used for this purpose for over a hundred years. It allows to identify late stages of the disease, when bone tissue is affected. In the last 20 years many new imaging modalities, such as ultrasonography (US), computed tomography (CT) and magnetic resonance (MR), have been developed and became important diagnostic tools for evaluation of rheumatoid diseases. They enable the assessment and monitoring of early inflammatory changes. As a result, patients have earlier access to modern treatment and thus formation of destructive changes in joints can be markedly delayed or even avoided.