The terms degenerative joint disease (DJD) and osteoarthritis (OA) are often used interchangeably, but strictly speaking OA is a subset of DJD (Bennett D et al. 2012). I prefer to use the term DJD as to me it is a reminder that cartilage degeneration predominates with inflammation being a more minor component.

DJD may be primary or secondary. Most feline cases are primary (i.e., not associated with an obvious underlying disease) but secondary DJD is also well recognised with trauma and hip dysplasia most commonly reported.

This article provides a brief overview of feline DJD. Readers are encouraged to read a recent review (Bennett et al. 2012) for more detailed information.

DJD in Cats

Cats are not small dogs and degenerative joint disease is an excellent example of this, with feline clinical signs being more subtle and frequently interpreted as 'normal ageing' by owners.

 Studies suggest that 17—91% of cats have DJD. These include retrospective and prospective studies, and in most not all joints were radiographed so they may under estimate the true prevalence. The highest prevalence of 91% (Lascelles 2010b) was a cross sectional study of 100 cats from a single practice. Cats were selected randomly irrespective of clinical signs and age and all appendicular joints were radiographed. This study confirms that DJD is very common, although it must be remembered that not all cats with radiographic changes exhibit clinical signs of DJD.

 More common in older cats (65% > 12 yo).

 Clinical signs of DJD are primarily behavioural/lifestyle changes. Most owners think these changes are just a 'normal part of ageing' and thus do not report them to the veterinarian. Common clinical signs include: unwilling to jump, reduced height of jump, stiff gait, altered temperament (resents handling), inappropriate elimination, altered grooming.

 Bilateral DJD is common (73—78%), hence only a minority have clinically detectable lameness (4—17%).

 Clarke and Bennett (JSAP,06) showed a statistically significant improvement in the following 3 clinical signs in cats with DJD that were treated with meloxicam; unwilling to jump, reduced height of jump and stiff gait.

 Using mobility questionnaires as part of routine senior screening is a helpful tool in both the diagnosis and monitoring of cats with DJD. Each questionnaire should be tailored to reflect the specific clinical signs exhibited by that cat (e.g., reduced ability to jump onto window sill, difficulty negotiating cat door, reduced playing / stretching / scratching / hunting etc).

 Joints most commonly affected; elbow, hip, stifle.

Diagnosis of DJD

Relies on a combination of owner observations of changes in behaviour, altered mobility, a careful orthopaedic examination (with severe DJD there may be joint thickening, reduced range of movement and/or pain on joint manipulation), radiographs and response to a therapeutic trial. It is important not to rely on a single criterion such as radiographs, as changes on X-rays do not necessarily correlate with clinically significant disease (i.e., radiographs can be unremarkable in some cats with significant DJD, and radiographically abnormal joints are not always painful (Lascelles 2010c; Freire et al. 2011).

Tips for Cats with DJD: Use Multimodal Management

Handle with Care

Joint manipulation in cats with DJD may be painful, e.g., elbow DJD is common, so take care when holding or extending the elbow for IV drip placement or anaesthesia.

Discuss modifications to the home environment e.g., food and water bowls should be easy to access, consider steps/ramps to help the cat reach its favourite resting places and to access the cat door. Provide soft, comfortable bedding.

Manage Obesity

Obesity is now recognised as an endocrine disease. Rather than 'wear and tear' from increased weight bearing, its adverse effect on joints relates primarily to the release of inflammatory cytokines from adipocytes. An individual cat's calorie requirements for weight loss can vary considerably. Where possible calculate the number of calories the cat is currently eating, and reduce this amount by 10%. I find feeding canned food improves cat and owner compliance; it's a larger volume for the cat to eat and in my opinion it is less likely for owners to feed more than recommended as can easily happen when measuring kibble. Select either a reduced calorie, low fat therapeutic diet or a food designed to create a metabolic shift such as Hill's^TM Prescription Diet^TM m/d^TM. Weigh and body condition score the cat every 1–2 weeks and adjust the amount fed as needed to achieve no more than 1% body weight loss per week (e.g., a 5 kg must not lose more than 50 grams per week). More rapid weight loss increases the risk of hepatic lipidosis and should be avoided.

Therapeutic Foods

There is good evidence from prospective, randomized, placebo controlled blinded clinical trials that feeding a diet rich in omega-3 fatty acids, and specifically eicosapentaenoic acid (EPA), isbeneficial for managing OA in dogs (Vanderweerd 2012; Roesch et al. 2010a, 2010b; Fritsch et al. 2010a, 2010b). Omega-3 fatty acids are anti-inflammatory and may also ameliorate the progression of DJD through a nutrigenomic effect. In dogs EPA down regulates aggrecanase, the principal degradative enzyme in canine chondrocytes. In cats docosahexaenoic acid (DHA) is thought to have a similar effect (DHA is the bioactive omega-3 fatty acid in feline chondrocytes [Innes et al. 2008]).

There is a paucity of studies in the peer reviewed literature regarding therapeutic diets for cats with DJD. One study, using a diet containing EPA, DHA, green lipped muscle extract, chondroitin and glucosamine showed an objective increase in activity in cats with DJD compared to the control group. However subjective assessment by owners and vets did not detect a benefit (Lascelles et al. 2010).

Preliminary studies with another therapeutic food, show promise. Hill's^TM Prescription Diet^TM Feline j/d^TM, contains higher levels of omega-3 fatty acids (including DHA and EPA), plus methionine, manganese, and a reduced omega-6:omega-3 ratio. Two abstracts reported a subjective improvement in mobility by owners and vets (Fristch et al. 2010; Sparkes et al. 2010), and one showed reduced subjective clinical improvement with this diet (Bennett et al. 2012). In dogs, feeding canine j/d^TM has a dose sparing effect on concurrent carprofen dosage (Fritsch et al. 2010b), on average reducing the dose by 25%. Although a similar study has not been published in cats, one article (Lascelles, Robertson 2010) emphasizes the importance of non-drug treatments for DJD, with addition of drug therapy where appropriate. Given cats' sensitivity to NSAIDs, anything that might reduce the reliance on, or dosage of, NSAIDs would seem advantageous.

Other Nutraceuticals?

Other nutraceuticals (e.g., glucosamine, green lipped muscle extract) are currently unproven in their efficacy for cats with DJD, but anecdotally they may help some cats and the risk of side effects is low.

NSAIDS and Other Analgesics

Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used to help manage pain associated with DJD. However consideration must be given to any other diseases that may affect the safety of NSAIDs. Readers are referred to recent detailed guidelines on NSAID use in cats (Sparkes et al. 2010). My recommendation is to select a NSAID that is metabolized by hepatic oxidation (vs glucuronidation) such as meloxicam. Blood pressure, haematology, full serum biochemistry and urinalysis should be checked prior to starting NSAIDs and kidney and liver function should be monitored regularly during therapy. Oral Metacam (Boehringer Ingelheim) is licensed for long term use in several geographies. The dose should be accurately titrated using the syringe supplied and mixed in canned food (so the cat only gets a dose if it is eating). Calculate the dose based on lean body weight. I usually skip the loading dose on day 1, starting at the recommended maintenance dose and weaning down to the minimum dose needed to keep the cat comfortable (often around the 0.025 mg/kg/day, which is lower than the manufacturers recommended dose). Some cats can be maintained on an alternate day schedule. Do not use NSAIDs if the cat is dehydrated, if anorexia/vomiting/renal deterioration develops or if it is on concurrent corticosteroids, diuretics or ACE-inhibitors.

Avoid corticosteroids as they reduce proteoglycan synthesis and may hasten cartilage degradation.

Opiates can be considered, especially in patients where NSAIDs are contra indicated or where additional multimodal analgesia is needed. Buccal pouch buprenorphine 0.01–0.03 mg/kg q 6–8 hours, taper to the minimum dose needed (may cause constipation). Alternatively tramadol 1—4 mg/kg PO BID, or for an average weight cat quarter of 50 mg PO BID (limited vet experience, use with caution and start at lower end of dosage).

Gabapentin or amantadine could also be considered although clinical experience with the latter is limited. See Lascelles and Robertson 2010, for more information regarding analgesia in cats with DJD.

Stem Cell Therapy

Stem cell therapy from autologous adipose derived mesenchymal stem cells has been anecdotally reported. However with current techniques it is questionable whether there is any 'regeneration' of joint tissues (Lascelles, Robertson 2010).

Physical Rehabilitation

Currently this is not a well-established option for cats with DJD, but given its value in canine patients, it is an area that deserves more attention.

References

References are available upon request.