Causes of Feline Arthritis
Arthritis refers to inflammation of one or more joints. It can be degenerative or inflammatory, and each of these general categories involves several sub-categories or types. The nomenclature can be confusing, because all arthritis involves some degree of inflammation. However, the primary cause of “degenerative” arthritis is not inflammation, while the main cause of “inflammatory” arthritis is. Regardless of cause or type, the end results of arthritis are the same: moderate to crippling pain and loss of normal joint function. Here’s a general overview of arthritis in cats.
- I. Degenerative (noninflammatory) Arthritis. Degenerative or noninflammatory arthritis, also called degenerative joint disease (DJD) and osteoarthritis (OA), is the most common type of arthritis in domestic cats. It’s an inevitably progressive and irreversible disease of slow joint and cartilage deterioration.
- A. Primary. Primary degenerative arthritis is uncommon in cats.
- B. Secondary. Most of the time, degenerative feline arthritis develops secondary to another inciting event or condition, such as acute or chronic trauma, which interferes with the biomechanical forces on affected joints. Physical injury – especially to the cartilage that connects joint bones (articular cartilage) - causes chemicals called inflammatory mediators to be released. These substances break down the connective cartilage matrix faster than it can be rebuilt, which leads to joint degeneration and lots of pain. The events that trigger the release of these chemicals typically fall into one of two categories: 1) abnormal forces on normal joints; or 2) normal forces on abnormal joints. Degeneration and collapse of the joint space damages the joint’s mechanical integrity and causes bone remodeling. As the joint breaks down, bony outgrowths form, intensifying the cat’s discomfort.
- 1. Abnormal forces on normal joints can be caused by sprains, fractures, obesity, aging, poor nutrition, trauma and many other things.
- 2. Normal forces on abnormal joints can be caused by elbow and hip dysplasia, osteochondrosis dissecans, patellar luxation, ununited anchoneal process, fragmented coronoid process, cranial cruciate ligament rupture and other congenital or genetic conformational defects.
- II. Inflammatory Arthritis. Inflammatory arthritis, also called inflammatory joint disease, can be infectious or noninfectious.
- A. Infectious. Infectious inflammatory arthritis is caused by bacteria, fungi, viruses, rickettsia or other microscopic organisms. Tick-borne diseases, like Rocky Mountain Spotted Fever, Lyme Disease and Ehrlichiosis, can contribute to infectious arthritis. Bacterial joint infections can be innocuated by injections, joint taps, surgical procedures, animal or reptile bites and other open or penetrating wounds. Fungal, viral and rickettsial causes of infectious arthritis are uncommon in cats.
- B. Noninfectious. Noninfectious inflammatory arthritis usually involves the immune system and affects multiple joints. For some reason, the cat’s immune system attacks its own cartilage and joints.
- 1. Erosive. Noninfectious arthritis can erode joints and cartilage, causing severe leg and paw deformities. Rheumatoid arthritis, plasmacytic-lymphocytic synovitis and systemic lupus erythematosus can contribute to erosive noninfectious arthritis.
- 2. Nonerosive. Noninfectious arthritis can also cause inflammation and pain without eroding joint and cartilage tissue. This isn’t common in cats.
Feline arthritis is hard to prevent. The progression of degenerative arthritis can be delayed if the cause is resolved. Weight management is probably the most important factor. Obese cats should be on a calorie-restricted diet under veterinary supervision. Supplements can help manage arthritis pain and may delay joint damage. Affected cats should always have a comfortable sleeping area that doesn’t require excessive jumping to reach.