Arthritis is an inflammation of any joint in the body, and the inflammation can have many causes. Your pet can develop arthritis due to aging, wear and tear on the joints, or a ruptured ACL in the knee.
The most common type of arthritis is osteoarthritis. The chronic form of this disease is called degenerative joint disease (DJD). It is estimated that 20% of dogs older than one year of age have some form of DJD. One study showed that 90% of cats over 12 years of age had evidence of DJD on x-rays.
Other causes of the inflammation can be infectious. Septic arthritis is caused by a bacterial or fungal infection. Lyme disease or Ehrlichia infection can also cause arthritis. Auto-immune diseases, or what is now called immune-mediated diseases, such as Lupus, can cause swollen, painful, and inflamed joints. More rarely, tumors can cause arthritis.
Treatment for arthritis should be directed to the inciting cause, if possible. DJD may be treated with NSAIDs (non-steroidal anti-inflammatory drugs), pain medication such as Tramadol, cartilage protective agents such as glucosamine or Adequan, acupuncture, or as a last resort, steroids. In general, it is recommended to use NSAIDs developed for pets (not people) as they are likely to cause ulcers in dogs. Most NSAIDs cannot be used in cats.