PATHOPHYSIOLOGY
Osteoarthritis may be categorized as primary or secondary. In primary osteoarthritis, no clear underlying cause is present.
With secondary osteoarthritis, an underlying cause can be implied, such as hip dysplasia or previous trauma. In one study,
half of the cats with osteoarthritis had an identifiable or historical cause, including radiographically identified hip dysplasia.1 In another study by the same researchers, 71% of cats had no obvious cause and were classified as having primary, or idiopathic,
osteoarthritis.5
CLINICAL SIGNS
Compared with the radiographic features of feline osteoarthritis, the clinical signs of feline osteoarthritis are not well-documented.
Unlike in dogs, lameness is not common in cats with DJD or osteoarthritis.1,5 Because of cats' small size and their innate agility, they can often cope with severe orthopedic disease. In addition, bilateral
involvement is common, which makes lameness difficult to detect. It is also notoriously difficult to elicit pain on clinical
examination in some cats.
In one clinical study, 28 cats that had historical or clinical evidence of osteoarthritis, or both, together with radiographic
evidence of osteoarthritis were recruited for a prospective study.5 Their median age was 11 years. In addition to the cats' undergoing a clinical examination by a veterinarian, the owners
filled out a questionnaire on their cats' general demeanor, food intake, and lameness. On physical examination, periarticular
thickening was a common finding but decreased range of motion was not. Crepitus was not detected, and synovial effusions were
seldom present. Cats were treated with oral meloxicam for one month and reevaluated. Most owners thought their cats improved,
and the most common clinical sign that improved was the willingness to jump and the height of the jump. Improvement of the
stiff gait seen in many cats at the beginning of the study was also significant.5
Table 1: Signs of Osteoarthritis Clients Should Watch for in Their Senior Cats
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Clinical experience suggests that the behavioral changes that accompany osteoarthritis may be either insidious and easily
missed or assumed to be inevitable with advancing age, so the owner does not seek veterinary advice. Because of a pet cat's
lifestyle, lameness or exercise intolerance is not a common owner complaint. Changes in behavior such as decreased grooming,
a reluctance to jump up on favorite places, an inability to jump as high as before, and soiling outside the litter box should
prompt the veterinarian to look for sources of chronic pain (Table 1). Other changes that owners report are altered sleeping habits (an increase or decrease), withdrawing from human interaction,
hiding, and a dislike of being stroked or brushed.
Inactivity, which may result from chronic joint pain, is much more difficult to determine in cats than in dogs since cats
naturally sleep a lot and are often solitary. In many cases, the owners are not home all day to monitor their cats' activity
levels and may not know whether they have changed. Activity monitors attached to cat collars and harnesses have been used
to monitor daily movement in cats,6,7 including in cats with osteoarthritis during treatment with oral meloxicam or placebo.7 In that study, the activity counts increased with five days of nonsteroidal anti-inflammatory drug (NSAID) treatment, suggesting
alleviation of musculoskeletal discomfort.
It is common for owners and veterinarians not to realize how affected a cat was until they see dramatic improvements after
treatment, emphasizing that analgesic trials may sometimes be the only way to confirm that pain was present.
TREATING OSTEOARTHRITIS
Osteoarthritis treatment falls into three categories: lifestyle changes, pharmacological intervention, and nonpharmacological
intervention.
Lifestyle changes
Much of the supportive management recommended for osteoarthritis in dogs, such as weight loss and controlled exercise, is
applicable in cats but is often more difficult to implement. Overweight cats should be placed on a carefully monitored weight-loss
program; several good commercial diets are available to achieve set goals. With creative use of toys and owner participation,
exercise can be encouraged in cats.
Chronic pain may prevent some cats from grooming, and owners must perform this task, although the cats may resent this until
pain is reduced to a tolerable level. Environmental modifications can simplify a cat's daily routine, such as placing food
bowls and litter boxes in positions that do not require leaping or jumping. If cats cannot leap onto favorite resting places
such as window ledges and cat towers, it impacts their quality of life. Owners can construct ramps and steps so cats may still
reach these spots.
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