Understanding of Rare Inflammatory Arthritis in Comparison to Classical Inflammatory Arthritis : Tissular Observations and Immune Infiltrate Characterization : the UTOPIC Project

Inclusion Criteria

• •For all participants:
• •* Signed consent form
• •* Patients over 18 years old
• •* Affiliated with a social security scheme
• •For cases:
• •* Referred for arthritis or bursitis occurring in the context of a rare systemic autoimmune disease (SAID) or drug-induced toxicity.
• •* Presenting at least one clinical arthritis with synovial thickening confirmed by ultrasound (grade ≥2 in B-mode) and Doppler inflammation of grade ≥1, or synovial thickening ≥B2 associated with joint effusion.
• •For bursitis: thickening ≥2mm of at least one periarticular bursa on ultrasound associated with Doppler inflammation of grade ≥1, or synovial thickening ≥2mm associated with joint effusion, with clinical evidence of inflammatory involvement.
• •\*For the control group:
• •For arthritis:
• •Presenting clinical arthritis with synovial thickening confirmed by ultrasound (grade ≥2 in B-mode (B2)) and Doppler inflammation of grade ≥1, or synovial thickening ≥B2 associated with joint effusion.
• •Diagnosed, according to disease-specific classification criteria, with either rheumatoid arthritis (according to ACR/EULAR 2010 criteria), axial or peripheral spondyloarthritis (according to ASAS 2009 criteria), psoriatic arthritis (according to CASPAR criteria), or reactive arthritis based on clinician assessment.
• •For bursitis:
• •Thickening ≥2mm of at least one periarticular bursa on ultrasound associated with Doppler inflammation of grade ≥1, or synovial thickening ≥2mm associated with joint effusion.
• •Meeting the ACR/EULAR 2012 criteria for polymyalgia rheumatica.