The development and validation of a new diagnostic sonographic enthesitis score for psoriatic arthritis: Diagnostic Ultrasound Enthesitis Tool (DUET).

Objective

The Diagnostic Ultrasound Enthesitis Tool (DUET) study aimed to develop and validate a new sonographic scoring system for enthesitis to aid PsA diagnosis.

Methods

We prospectively enrolled patients with early PsA, psoriasis without arthritis (PsO), and non-inflammatory musculoskeletal symptoms as controls (CTL) from 17 centers. A standardized ultrasound assessment of 16 entheseal sites was performed and images were centrally scored by three blinded readers for inflammatory and structural entheseal lesions. Using a stepwise approach with logistic regression models stratified by age, we identified optimal lesion combinations, weightings, and entheseal sites for distinguishing PsA from CTL. Age-specific cut-off points were selected to maintain specificity above 70%. Performance was assessed in a validation cohort of PsA and CTL.

Results

We included 213 PsA, 100 PsO, and 106 CTL in the discovery cohort. The final DUET score combined weighted inflammatory (hypoechogenicity + thickening + Doppler grade x 2) and structural (enthesophyte grade + erosion x 3) scores at three entheseal sites: Achilles, proximal patellar tendon insertion, and triceps. Age stratification (≤55 vs. >55 years) improved discriminative performance. In the discovery cohort, DUET achieved an AUC of 0.65, with specificity of 73-74% and sensitivity of 47-49%. In an external validation cohort (101 PsA, 69 CTL), specificity improved to 74-100% with similar sensitivity (49-52%). Sensitivity increased up to 63% in patients with tender entheses.

Conclusion

DUET is a novel, externally validated sonographic enthesitis score that could support the diagnostic assessment of patients with early PsA, particularly in individuals with tender entheses.