Disease measurement--enthesitis, skin, nails, spine and dactylitis.

Outcome measurement is a key part of study design but presents particular challenges in spondyloarthropathy. Enthesitis and dactylitis are typical features of spondyloarthropathy and validated scoring systems for both are available, although the majority of enthesitis outcome measures are validated in ankylosing spondylitis (AS) only. Assessment of axial disease is well researched in AS and composite outcome measures are routinely used. However, assessment of axial disease in predominantly peripheral arthritis, such as psoriatic arthritis, is problematic and under-researched. Extensive research in dermatology has provided multiple outcome measures for skin psoriasis. The psoriasis area and severity index (PASI) remains the most common outcome measure used, despite the fact that significant problems exist with this scale and that newer scoring methods and modifications of the PASI show better validity. Nail psoriasis is accurately measured by detailed scoring systems but these can be time-consuming.