Objective. To assess currently available tools for measurement of enthesitis and to develop a new instrument specifically for use in psoriatic arthritis (PsA). Methods. Twenty-eight patients with PsA underwent clinical assessment over a period of 6 months after change of disease-modifying therapy, usually to methotrexate. Measures of enthesitis included the Mander Enthesitis Index (MEI), the Maastricht Ankylosing Spondylitis Enthesitis Score, the Major index, and the Gladman index. Data from these assessments were used to develop a new enthesitis index, the Leeds Enthesitis Index (LEI).Results. An iterative process of data reduction enabled derivation of the LEI index, which consisted of 6 sites: right and left Achilles insertions, medial femoral condyles, and lateral epicondyles of the humerus. All measures showed significant change from baseline but only the LEI and Gladman indices showed a large effect size. All indices demonstrated a floor effect (a score of 0 when the MEI is >0) but this was minimal for the LEI index. All indices correlated strongly with each other and other measures of disease activity. Conclusion. The LEI is a new enthesitis index designed for use in PsA. It shows good test characteristics that suggest it will be a robust and reliable assessment tool. We suggest that it be adopted for use in any randomized controlled trials and longitudinal observation cohorts involving patients with PsA.

Two new composite measures to assess disease activity in PsA have been developed. Further testing in other datasets, including comparison with existing measures, is required to validate these instruments.

MRI images demonstrate widespread abnormalities in digits of people with psoriatic arthritis. Tender dactylitic digits have more abnormalities than other digits but the relationship between clinical and MRI scores is not strong.

The spondyloarthropathy classification criteria continue to be an area of development. This is most apparent in juvenile arthritis and psoriatic arthritis. The latter is currently undergoing intense scrutiny to develop classification criteria and outcome measures.