Defining enthesitis in spondyloarthritis by ultrasound: results of a Delphi process and of a reliability reading exercise.

Objective: To standardize ultrasound (US) in enthesitis.

Methods: An initial Delphi exercise was undertaken to define US-detected enthesitis and its core components. These definitions were subsequently tested on static images taken from spondyloarthritis patients in order to evaluate their reliability.

Results: Excellent agreement (>80%) was obtained for including hypoechogenicity, increased thickness of the tendon insertion, calcifications, enthesophytes, erosions, and Doppler activity as core elementary lesions of US-detected enthesitis. US definitions were subsequently obtained for each elementary component. On static images, the intraobserver reliability showed a high degree of variability for the detection of elementary lesions, with kappa coefficients ranging from 0.13-1. The interobserver kappa values were variable, with the lowest kappa coefficient for enthesophytes (0.24) and the highest coefficient for Doppler activity at the enthesis (0.63).

Conclusion: This is the first consensus-based US definition of enthesitis and its elementary components and the first step performed to ensure a higher degree of homogeneity and comparability of results between studies and in daily clinical work.