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, 16:18, 3 March 2011
*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
**[[Musculoskeletal Terminology - Pathology|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 [[Pigmentation - Pathology#Haemosiderin|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|Systemic lupus erythematosus (SLE)]]====
*Occurs in dogs
*Clinical signs:
**Anaemia
**Thrombocytopaenia
**[[Muscles Inflammatory - Pathology#Myositis|Polymyositis]]
**[[Kidney Glomerular Disease - Pathology#Glomerulonephritis|Glomerulonephritis]]
====In chronic diseases====
*E.g. pyometra, otitis externa, [[Endocarditis|endocarditis]], [[:Category:Intestine - Inflammatory Pathology|enteritis]]
*Can lead to immune complex deposition in joints
====Gout====
*Occurs in humans, reptiles and birds (have no uricase enzyme)
*The urate triggers inflammation
[[Category:Arthritis]]