The incidence of chronic pain in cats is not well-documented but is associated with many conditions, including osteoarthritis, cancer, interstitial cystitis, dental and gum disease, and long-standing dermatitis and wounds. It is only recently that veterinarians have begun to appreciate what the true incidence of osteoarthritis, sometimes called degenerative joint disease, might be in cats. It appears to be much more common than previously thought and could be a major cause of discomfort, especially in senior (> 10 years of age) cats.
DEGENERATIVE JOINT DISEASE VS. OSTEOARTHRITIS
Although the terms degenerative joint disease and osteoarthritis are commonly used interchangeably in the veterinary arena, a distinction has been made between the two.1 Degenerative joint disease (DJD) is a general term used to describe any degenerative change in a synovial, cartilaginous, or fibrous articulation in the skeleton. Osteoarthritis, however, is a pathologic change of a diarthrodial synovial articulation and includes deterioration of articular cartilage, osteophyte formation, bone remodeling, soft tissue changes, and low-grade nonpurulent inflammation. Not all radiographic changes are correlated with a clinical problem. As veterinarians, we are most interested in changes that have a negative impact on a cat's life because of pain and discomfort or because the cat can no longer perform normal functions such as jumping.
In one of the first studies designed to determine the prevalence of DJD in cats, radiographs of 100 cats more than 12 years old (taken as part of a diagnostic work-up for multiple reasons) were retrospectively reviewed,2 and 90% of them showed radiographic evidence of DJD. When the medical records of these cats were examined, only four contained any mention of DJD, but severe DJD of the vertebral column (termed spondylosis deformans) was sometimes associated with neurologic disease. The key question from this study was "Did the failure to observe clinical signs truly represent a lack of clinical signs in the presence of radiographic findings or a failure to recognize signs?"
Obesity and osteoarthritis: Is there a link in cats?
As in dogs,3 the radiographic findings of osteoarthritis do not always correlate well with clinical function. In a radiological study involving cats of all ages, 22% showed evidence of radiographic osteoarthritis, and when patient records were consulted, 33% of these cats also had clinical signs.4 Affected cats were significantly older than the control population. These authors also suggested that there may be little correlation between radiographic and clinical findings or that clinical signs of osteoarthritis in cats are not easily recognized.
In a recent study at a university referral hospital, the prevalence of radiographic signs of DJD was 33.9%, and the prevalence of clinical signs was 16.5%, with most affected cats being 10 years of age or older.1 These authors further classified their findings into DJD and osteoarthritis, the second being less common.
The elbow joint was the most commonly affected joint in some published studies.1,2,4,5 However, when osteoarthritis (rather than DJD) was specifically described, the hip joint was most frequently affected.1 Many cats have multiple affected joints, and bilateral involvement is common.