Rheumatoid Arthritis

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Rheumatoid Arthritis-Brian Catchpole RVC 2008


  • Type IV hypersensitivity: CD4 Th-1 cell mediated.
  • Macrophages phagocytose self antigens and can present peptides on their MHC Class II molecules. The autoreactive TH-1 cells release IFN-gamma which activates macrophages to release prostaglandins, MMP enzymes and TNF-alpha (pro-inflammatory mediator), see diagram. These cytokines cause inflammation and tissue destruction.

  • Occurs in the dog, mainly smaller breeds
  • Uncommon
  • Progressive erosive polyarthritis
  • Mostly involves elbows, stifles, carpal and tarsal joints
  • Grossly:
  • Histologically:
    • Hyperplasia of lining cells
    • Proliferative synovitis
    • Synovial membrane has fibrin deposits
    • Lymphoid and plasma cell infiltration
    • Surrounding haemorrhagic areas
    • Macrophages containing haemosiderin
    • Connective tissue may contain foci of necrosis
    • Areas of erosion of peripheral articular cartilage and underlying subchondral bone
  • Pathogenesis:
    • May involve deposition of immune complexes within joints
    • Substances degrading cartilage are released by synovial cells and macrophages involved in pannus formation