Reliability of ultrasound assessment of elementary lesions in psoriatic arthritis and development of a reference dactylitis atlas.

Abstract

Ultrasound (US) is a valuable tool to detect inflammation in peripheral psoriatic arthritis (pPsA). This multicentre study assessed the intra- and inter-reader reliability of US-detected elementary lesions in peripheral psoriatic arthritis (pPsA) and evaluated the impact of standardized training on reliability, as a first step to guide multicentre assessment in the APACHE cohort. A cross-sectional study was conducted to analyse the reliability of pPsA US lesions, as a first step in an ongoing predictive cohort (APACHE, NCT03768271) study. Three web-based reliability exercises were carried out between 2020 and 2024. Inter-rater and intra-rater reliability were assessed using Light's kappa (κ). During the third reliability exercise, a reference atlas of elementary US lesions in dactylitis was developed. Experienced and trainee sonographers from 30 recruiting centres participated into the study. In step 1, intra-reader kappas were moderate-to-good for synovitis (0.50-0.80), tenosynovitis (0.51-0.63), enthesitis (0.62-0.73), and poor for dactylitis (0.31-0.47); inter-reader kappas were lower for synovitis (0.32-0.70), tenosynovitis (0.40-0.49), enthesitis (0.47-0.60) and dactylitis (0.13-0.24). In Step 2, reliability improved notably in expert and trainees except for dactylitis [intra-reader: synovitis (0.81-0.90), tenosynovitis (0.66-0.83), enthesitis (0.61-0.81), dactylitis (0.37-0.47); inter-reader: synovitis c(0.72-0.84), tenosynovitis (0.55-0.76), enthesitis (0.37-0.59), dactylitis (0.12-0.30)]. Step 3 achieved moderate-to-good reliability for dactylitis (intra 0.69-0.80, inter 0.46-0.68). An atlas was produced based on expert consensus and lesion identification rates among sonographers. Standardized training was associated with a marked improvement in intra- and inter-reader reliability for the assessment of elementary pPsA lesions. The consensus-based US atlas provides practical guidance for identifying challenging dactylitis-related lesions in clinical and research settings.