Immune‐based erosive inflammatory joint disease of the dog: canine rheumatoid arthritis.

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Abstract
The pathological features of 30 cases of canine rheumatoid arthritis are described. The principle pathological feature is a chronic symmetrical polysynovitis. The pathological features of the joints varied in severity. The synovial membrane generally showed villous hypertrophy with aggregates of lymphocytes and plasma cells. Destruction of articular cartilage and bone occurred in association with a replacement granulation tissue which often produced a pannus over the articular surface. Immunofluorescence studies demonstrated complexes of IgG or IgM with C3 in synovial lining cells, macrophages, blood vessel walls and free in the extracellular tissues. IgG and IgM producing plasma cells were also common. Fibrinogen deposits were extensive. The immunofluorescence findings were non‐specific but support the concept of an immune complex mediated inflammation within the joints. Investigations for bacterial, mycoplasmal and viral infections of the joints were negative.