Patient with undifferentiated arthritis and the presence of anti-citruline (anti-CCP) antibodies are at high risk to develop RA. The presence of anti-CCP is associated with a higher rate of erosion and a higher risk of progressive and severe RA.

The investigators have demonstrated in the CIERA study that MTX/IFX combination therapy is superior to MTX alone to reduce MRI signs of synovitis and bone edema and is clinically more effective.

The immunopathogenesis of undifferentiated arthritis is poorly understood. However, synovial studies from patients with early arthritis suggest that UA and RA may share common immunopathogenic mechanisms. One biopsy study of asymptomatic joints in patients with early arthritis demonstrates synovitis in more than half of the joints samples with prominent T cell and macrophage infiltration, similar to Rheumatoid Arthritis (RA).

Thus intensive treatment with anti-TNF antibodies (infliximab) may have an impact on multiple immune mechanisms driving synovitis in undifferentiated arthritis and may influence the clinical outcome.

Recently, Methotrexate has been demonstrated to improve the course of undifferentiated arthritis and prevent the development of RA. Short regimen of more intensive therapy with Infliximab could alter the radiological, immunopathological and clinical outcome.

not necessary

Inclusion Criteria:

Diagnosis of UA Absence of American College of Rheumatology (ACR) criteria Active UA defined by a swollen joint count ≥ 1 and < 4 Positive anti-CCP Disease duration < 2 years DMARDs naive No chronic treatment with steroids (> 3 months), if needed washout of 4 weeks NSAIDs stable

Exclusion Criteria:

Other rheumatic inflammatory diagnosis Contraindication to MRI (pace-maker, etc.) Congestive heart disease Active or latent tuberculosis