INTRODUCTION: Persistent pain is a major concern for patients with psoriatic arthritis (PsA). Pain may be due to inflammatory activity or augmented central pain processing. Unawareness of the origin and mechanisms of pain can lead to misinterpretation of disease activity (by composite scores) and erroneous treatments. Ultrasonography (US) is a highly sensitive method to detect tissue inflammation. Evaluating pain mechanisms in relation to US measures may prove valuable in predicting response to treatment in PsA.

AIMS: To study the association and prognostic value of pain mechanisms, ultrasonic activity and clinical outcomes in patients with PsA who intensify antirheumatic treatment.

METHODS AND ANALYSES: 100 participants >18 years of age with PsA who initiate or switch antirheumatic treatment (biologicals and/or conventional synthetic disease-modifying antirheumatic drugs (DMARDs)) will be prospectively recruited from outpatient clinics in Copenhagen. All data (demographics, clinical, imaging, blood samples and patient-reported outcomes) will be collected at baseline and after 4 months. Pain is assessed by the PainDETECT Questionnaire, Visual Analogue Scale for pain, Swollen to Tender Joint Count Ratio, Widespread Pain Index and tender point examination. The association between pain variables and clinical/US characteristics will be described by correlation analyses. The predictive value of pain measures and baseline US scores on treatment response will be analysed with regression models. Outcomes are composite and clinical, as well as patient reported.

ETHICS AND DISSEMINATION: The study is approved by the ethics committee of the Capital Region of Denmark (H-15009080) and has been designed in cooperation with patient research partners. The study is registered at clinicaltrials.gov (number NCT02572700). Results will be disseminated through publication in international peer-reviewed journals.

TRIAL REGISTRATION NUMBER: NCT02572700, Pre-results.