The Development and Validation of a Diagnostic Ultrasound Enthesitis Score (DUET) for Psoriatic Arthritis

Objectives Enthesitis is a key lesion in psoriatic arthritis (PsA). The Diagnostic Ultrasound Enthesitis Tool (DUET) study aimed to develop and validate a novel sonographic scoring system for enthesitis to aid PsA diagnosis. Methods We prospectively enrolled patients with early PsA, psoriasis alone, and people with non-inflammatory musculoskeletal symptoms as controls, across 17 centers. Participants underwent ultrasound assessments of 16 entheseal sites in the upper and lower extremities, performed by local sonographers. Images were centrally reviewed by 3 readers to derive a consensus score for inflammatory lesions (hypoechogenicity [0-1], thickening [0-1], power Doppler [PD, 0-3]) and structural lesions (calcification [0-3], enthesophyte [0-3], erosion [0-1]). Using a stepwise approach with logistic regression models stratified by age, we identified optimal combinations of lesions and their weighting, and entheseal sites that maximized the ability to distinguish PsA from controls. Data from the discovery cohort, supplemented by an existing validation dataset, were used to determine cut-off points that optimize sensitivity while maintaining specificity above 70%. We further evaluated the association between the DUET score and PsA disease activity measures. Results We analyzed 213 patients with PsA (mean duration 1.9±3.4 yrs), 100 with psoriasis and 106 controls. The mean age was 49.9±14.6 and 53.7% were females. Tenderness at ≥1 entheseal site was observed in 70% of PsA patients, 49% of controls and 33% of psoriasis. Initial evaluation of 4 inflammatory and 5 structural sub-scores across 16 entheseal sites yielded 48 candidate scores. Stratification by age improved discriminative performance. The best performing score (DUET score), comprising inflammatory (hypoechogenicity+thickening+2×PD) and structural (enthesophyte+3×erosion) (Figure 1A), sub-scores at the Achilles, patellar tendon insertion, and triceps tendon, achieved an overall AUC of 0.65. Age-specific cut-offs (at age 55) yielded specificity of 73-74% and sensitivity of 47-49% (Figure 1B). In the validation cohort (101 PsA, 69 controls), specificity improved to 74-100% with comparable sensitivity (49-52%). Sensitivity increased up to 63% in patients with tender entheseal sites (Figure 1C). The mean DUET score was significantly higher in PsA compared with controls and psoriasis (9.07 vs 5.48 and 6.38, respectively; p<0.01) (Figure 1D). Scores were elevated among obese patients, those with tender entheses, and those about to escalate PsA therapy. Conclusion DUET is a newly developed sonographic tool that may assist in the diagnosis of PsA, particularly among individuals with tender entheseal sites. The findings suggest that large joint enthesitis is a universal feature of early PsA.