Canine Arthritis - Rheumatoid Arthritis
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| Definition | Osteoarthritis | Other Types of Arthritis |
| Symptoms | Rheumatoid Arthritis | Risk Factors / Diagnosis |
About Rheumatoid Arthritis in Dogs
Aside from osteoarthritis, there are six different types of canine arthritis:
Canine Rheumatoid Arthritis (otherwise known as Immune-mediated Arthritis). Canine rheumatoid arthritis is a noninfectious, inflammatory, immune-mediated disease. Rheumatoid arthritis in dogs is not very common, and it has no sex predilection. It occurs mainly in small and toy breed dogs. Rheumatoid arthritis has been reported to occur in dogs from 8 months to 8 years of age, with the most common occurrences being in dogs 2 to 6 years of age. Rheumatoid arthritis is a chronic problem that can result in joint deformity.
Rheumatoid arthritis is caused by an overreaction of the immune system due to the body misunderstanding itself. In rheumatoid arthritis, the body mistakes some of its own protein for foreign protein and makes antibodies against it. These antibodies are collectively called the "rheumatoid factor." The antibodies and protein form immune complexes, which are then deposited in the joint, triggering inflammation. With rheumatoid arthritis, the body tries to rid itself of these hurtful immune complexes, but manages only to create more damage to the joint. Eventually the cartilage and even the bone in the joint are worn away.
Causes of Rheumatoid Arthritis in Dogs
The specific cause of rheumatoid arthritis is unknown. It has been speculated that canine distemper virus and the body's immune response to this virus may play a role in the development of canine rheumatoid arthritis. Other possibilities are that type II collagen serves as an autoantige, and that some type of altered host immunoglobulin (IgG) is the inciting antigen that stimulates the immune response. Autoantibodies subsequently are formed and directed against the altered host immunoglobulin. These autoantibodies are called rheumatoid factors. The autoantibodies form complexes with the altered IgG molecules, and these immune complexes are deposited in the synovium of the joints. Inflammatory mediators are then activated, leading to a severe, erosive polyarthritis known as rheumatoid arthritis.
Symptoms of Rheumatoid Arthritis
X-rays, biopsies, and the history of the pet often lead a veterinarian to suspect the disease. A special blood test can be done to look for the rheumatoid factor. The synovial fluid, present in the joints of the dog, may be analyzed to show changes. Cells involved in inflammation, which may be present in large numbers, may be analyzed to show changes. The fluid is usually of a thinner consistency than normal and cloudy instead of clear.
Some symptoms are visible to the naked eye. Dogs with rheumatoid arthritis often present with discomfort or pain in their joints. This can be seen as a shifting leg lameness or difficulty rising, walking up steps, and impaired ambulation. The joints that are most commonly affected are the carpal and tarsal joints. Affected joints may display signs of inflammation, such as excessive warmth and/or swelling on palpation. Anorexia and malaise often are observed by the owner. The dog also may display a persistent fever. Some dogs with rheumatoid arthritis also have kidney disease, enlarged lymph nodes, tonsillitis, and pneumonia.
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