The main objective is to assess if a treat-to-target strategy implementing structured imaging assessments leads to better patient outcome in terms of sustained remission compared to a conventional treat-to-target strategy in psoriatic arthritis.

Main inclusion criteria are: >18 years of age, Clinical diagnosis of psoriatic arthritis (PsA), Fulfillment of ClASsification of Psoriatic Arthritis (CASPAR) criteria, Indication for treatment with disease modifying anti-rheumatic drugs according to treating physician

Primary endpoint: Sustained remission, defined as Very Low Disease Activity (VLDA) at 16, 20 and 24 months

Secondary endpoints: Individual and composite disease activity measures and remission criteria, inflammation assessed by ultrasound, health related quality of life and adverse events.

Study design: A two-arm, parallel-group, single-blind, treatment strategy study where patients are randomized 1:1 to a conventional treat-to-target follow-up strategy with structured clinical assessment of disease activity or an imaging informed treat-to-target follow-up strategy with both structured clinical assessment of disease activity and structured imaging assessment of disease activity. Duration of follow-up is 24 months.

All patients are treated according to an algorithm based on current European recommendations. The conventional treatment target, applicable to both arms and the sole target in the conventional arm, is all of: Disease Activity index in Psoriatic Arthritis (DAPSA) remission (≤3), Enthesitis ≤1, Psoriasis Body Surface Area ≤3%

Intervention: A treat-to-target treatment strategy incorporating information from ultrasound assessment of joints, tendons and entheses (at every visit), and magnetic resonance imaging (MRI) of spine and sacroiliac (SI)-joints at baseline and 1 year, in addition to clinical information. Specifically, this means that these additional measures will be added to conventional treat to target:

• If evidence of enthesitis or axial inflammation on imaging the patient will progress directly to biological disease modifying antirheumatic drug in the treatment algorithm
• If evidence of ongoing inflammation (power Doppler>0) on ultrasound assessment of joints, tendons or enthesis, the patient will be classified as not having reached their treatment target

This project addresses the challenges associated with psoriatic arthritis (PsA), which is a diverse disease which is difficult to assess clinically. Ultrasound and magnetic resonance imaging (MRI) visualize inflammation that is not apparent on clinical examination, but whether treating patients according to these findings improves outcomes is unknown.

The main objective is to assess if a treat-to-target strategy implementing structured imaging assessments leads to better patient outcome in terms of sustained remission compared to a conventional treat-to-target strategy in psoriatic arthritis.

Primary endpoint: Sustained remission, defined as Very Low Disease Activity (VLDA) at all of the 16, 20 and 24 month visits.

Secondary endpoints include Individual and composite disease activity measures and remission criteria, inflammation assessed by ultrasound, health related quality of life and adverse events.

Study design: A two-arm, parallel-group, single-blind, treatment strategy study where patients are randomized 1:1 to a conventional treat-to-target follow-up strategy with structured clinical assessment of disease activity or an imaging informed treat-to-target follow-up strategy with both structured clinical assessment of disease activity and structured imaging assessment of disease activity. Duration of follow-up is 24 months.

All patients are treated according to an algorithm based on current European recommendations. The conventional treatment target, applicable to both arms and the sole target in the conventional arm, is all of: Disease Activity index in Psoriatic Arthritis (DAPSA) remission (≤3), Enthesitis ≤1, Psoriasis Body Surface Area ≤3%

Intervention: A treat-to-target treatment strategy incorporating information from ultrasound assessment of joints, tendons and entheses (at every visit), and magnetic resonance imaging (MRI) of spine and sacroiliac (SI)-joints at baseline and 1 year, in addition to clinical information. Specifically, this means that these additional measures will be added to conventional treat to target:

If evidence of enthesitis or axial inflammation on imaging the patient will progress directly to biological disease modifying antirheumatic drug in the treatment algorithm If evidence of ongoing inflammation (power Doppler>0) on ultrasound assessment of joints, tendons or enthesis, the patient will be classified as not having reached their treatment target

Inclusion Criteria:

1. Adult (>18 years of age)
2. Clinical diagnosis of PsA
3. Indication for treatment with DMARDs according to treating physician (including having attempted ≥2 non-steroidal anti-inflammatory drugs (NSAIDs) for a minimum of 4 weeks in total in predominantly axial and/or entheseal disease)
4. Fulfillment of CASPAR criteria for PsA

Exclusion Criteria:

1. Verified arthritis >1 year prior to inclusion
2. Previous DMARD treatment for PsA
3. Systemic glucocorticoid use within the last 3 months
4. Local glucocorticoid injections within the last 4 weeks
5. Major co-morbidities, including but not limited to relevant malignancies, severe diabetes mellitus, severe infections, uncontrolled hypertension, severe cardiovascular disease (NYHA class III or IV) and/or severe respiratory diseases and cirrhosis.
6. Indications of active or latent tuberculosis (TB) as assessed by chest radiograph and TB interferon gamma release assay (IGRA). Patients with documented adequately treated latent TB can be included.
7. Any other medical condition that according to the treated physician and/or local guidelines makes adherence to treatment protocol impossible
8. Abnormal renal function, defined as serum creatinine >142 µmol/L in female and >168 µmol/L in male, or estimated glomerular filtration rate (eGFR) <40 mL/min/1.73 m2
9. Abnormal liver function (defined as Aspartate Transaminase (AST) and/or Alanine Transaminase (ALT) >1.5 x upper normal limit), active or recent hepatitis
10. Significant anemia, leukopenia and/or thrombocytopenia
11. Inadequate birth control, pregnancy, and/or breastfeeding (current at screening or planned within the duration of the study)
12. Contraindications to magnetic resonance imaging
13. Severe psychiatric or mental disorders, alcohol abuse or other substance abuse, language barriers or other factors which makes adherence to the study protocol impossible
14. Established or suspected widespread-pain syndrome/fibromyalgia