- Design
- Prospective multicentre diagnostic development and external validation study
- Population
- Early PsA, psoriasis and non-inflammatory controls across 17 centres
- Primary outcome
- Discrimination of PsA from controls by ultrasound enthesitis score
- Effect
- Validation specificity 74–100%, sensitivity 49–52%; discovery AUC 0.65
The DUET study enrolled people with early psoriatic arthritis, psoriasis without arthritis and non-inflammatory musculoskeletal symptoms at 17 centres. Sixteen entheseal sites were scanned and centrally scored by blinded readers to build a diagnostic score.
The final score combines weighted inflammatory and structural findings at three sites — Achilles, proximal patellar tendon and triceps — with age-specific cut-offs. In the discovery cohort (213 PsA, 106 controls) the AUC was 0.65, specificity about 73% and sensitivity about 48%. In external validation (101 PsA, 69 controls) specificity was 74–100% and sensitivity 49–52%, rising to 63% when entheses were tender.
A three-site scan is quick, and a positive score adds weight to a PsA diagnosis. But with sensitivity around half, a negative scan does not exclude it. The score is a support to clinical judgement, not a replacement.
- Consider ultrasound of Achilles, patellar and triceps entheses when early PsA is uncertain.
- Treat a positive score as supportive, especially in people with tender entheses.
- Do not exclude PsA on a negative scan; sensitivity was about 50%.
- Use age-specific cut-offs, as degenerative changes rise with age.
Why it matters
Enthesitis is hard to judge clinically, and a standard short scan could make early PsA diagnosis more consistent.
The statistics, in plain English
An AUC of 0.65 means modest overall discrimination. High specificity with low sensitivity makes a test better at ruling in than ruling out.
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