Inflammatory polyarthritis secondary to deposition of immune complexes can produce erosive (destruction of articular cartilage and subchondral bone) or nonerosive (periarticular inflammation) joint disease. Rheumatoid arthritis, Greyhound polyarthritis, and feline progressive polyarthritis are examples of erosive arthritides. Systemic lupus erythematosus is the most common cause of nonerosive arthritis.
Clinical signs are lameness, multiple joint pain, joint swelling, fever, malaise, and anorexia. Clinical signs commonly wax and wane.
Diagnosis is aided by radiography, biopsy, arthrocentesis, and serologic testing. Radiography reveals periarticular swelling, effusion, and joint collapse plus subchondral bone destruction in erosive conditions. Joint fluid analysis will reveal elevated cell counts exceeding 3,000/mcL, composed primarily of normal polymorphonuclear cells. Biopsy of synovial tissue reveals mild to severe inflammation and cellular infiltrates. Serologic testing is performed for rheumatoid factor and antinuclear antibodies.
Treatment involves anti-inflammatory medications (eg, corticosteroids) and chemotherapeutic agents (eg, cyclophosphamide, azathioprine, or methotrexate). Prognosis is guarded because of relapses and inability to determine the inciting cause of the autoimmune reactions.