Psoriatic arthritis: imaging techniques.

Imaging techniques to assess psoriatic arthritis (PsA) include radiography, ultrasonography (US), magnetic resonance imaging (MRI), computed tomography (CT) and bone scintigraphy. The radiographic hallmark of PsA is the combination of destructive changes (joint erosions, tuft resorption, osteolysis) with bone proliferation (including periarticular and shaft periostitis, ankylosis, spur formation and non-marginal syndesmophytes). US has an increasing important role in the evaluation of PsA. In fact, power Doppler US is useful mainly for its ability to assess musculoskeletal (joints, tendons, entheses) and cutaneous (skin and nails) involvement, to monitor efficacy of therapy and to guide steroid injections at the level of inflamed joints, tendon sheaths and entheses. MRI allows direct visualization of inflammation in peripheral and axial joints, and peripheral and axial entheses, and has dramatically improved the possibilities for early diagnosis and objective monitoring of the disease process in PsA. MRI has allowed explaining the relationships among enthesitis, synovitis and osteitis in PsA, supporting a SpA pattern of inflammation where enthesitis is the primary target of inflammation. CT has little role in assessment of peripheral joints, but it may be useful in assessing elements of spine disease. CT accuracy is similar to MRI in assessment of erosions in sacroiliac joint involvement, but CT is not as effective in detecting synovial inflammation. Bone scintigraphy lacks specificity and is now supplanted with US and MRI techniques.