Rheumatoid arthritis (RA): Pathogenesis and Joint diseases features
• RA affects 1% of population, women > men
• Characterized by poly-articular joint pain, swelling, and stiffness, most commonly affecting the small joints (wrists, metacarpal-phalangeals). Joint involvement is bilaterally symmetrical.
• Extra-articular manifestations are often seen.
• Plasma cells often produce characteristic antibodies -> Anti-Cyclic Citrullinated Peptide (aCCP), Rheumatoid Factor (RF) in serum
• Non-specific Acute-phase reactants are also produced -> High serum CRP. ESR
• Stimulation of nerve endings in subchondral bone & synovial membrane (NOT in cartilage) -> Symmetrical, poly-articular arthralgia (joint pain), especially in small joints.
• Rate of inflammatory fluid accumulation in synovial joint capsule exceeds rate of fluid drainage -> Palpable Joint effusion (Swelling notable on Xray)
• Synovial enlargement forms palpable lumps in the joint -> Enlarged, "boggy" joints, esp carpal, MCP, PIP joints
• Physical narrowing of joint space decr joint mobility -> Incr joint stiffness, Decr Range of movement
• As cartilage and subcondral bone is eroded, continued usage / pressure on joints can mal-align, sublux, or collapse joints -> Joint Deformities. i.e. Swan-neck Boutonniere's ulnar drift of fingers, radial wrist deviation, etc
• Systemic inflammation + other mechanisms -> Extra-articular signs
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