Non-Infectious Arthritis

• No causative agent has been found
• Seem to be immune-mediated diseases

Erosive

Rheumatoid arthritis

• Occurs in the dog, mainly smaller breeds
• Uncommon
• Progressive erosive polyarthritis
• Mostly involves elbows, stifles, carpal and tarsal joints
• Grossly:
  • Marked villus hypertrophy of synovial membrane
  • Cartilage erosion
  • Pannus and periarticular osteophyte formation
  • In severe cases ankylosis
• 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

Non-erosive

Systemic lupus erythematosus (SLE)

• Occurs in dogs
• Clinical signs:
  • Anaemia
  • Thrombocytopaenia
  • Polymyositis
  • Glomerulonephritis

In chronic diseases

• E.g. pyometra, otitis externa, endocarditis, enteritis
• Can lead to immune complex deposition in joints

Gout

• Occurs in humans, reptiles and birds (have no uricase enzyme)
• The urate triggers inflammation