Clinical meaning
Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease primarily affecting the synovial joints. Autoantibodies (rheumatoid factor and anti-citrullinated peptide antibodies/anti-CCP) form immune complexes that deposit in the synovium, activating complement and recruiting inflammatory cells. CD4+ T cells, macrophages, and fibroblast-like synoviocytes proliferate, creating the pannus - a destructive inflammatory tissue that invades cartilage and subchondral bone. Pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6) drive joint destruction, while RANKL-mediated osteoclast activation causes periarticular erosions. RA characteristically presents as symmetric polyarthritis of small joints (MCP, PIP, wrist, MTP) with morning stiffness > 60 minutes. Extra-articular manifestations include rheumatoid nodules, interstitial lung disease, pericarditis, vasculitis, and Felty syndrome. Early aggressive treatment following the treat-to-target strategy (targeting remission or low disease activity) prevents irreversible joint destruction.