OSTEOARTHRITIS (OA) or Degenerative Joint Disease (DJD) is thought to be the most common cause of chronic pain in dogs and evidence is emerging of a similar picture in cats.
It’s hardly surprising, then, that it’s the focus of much effort by pharmaceutical, nutraceutical and nutrition companies in finding new and improved ways of managing the disease.
Combinations of therapies are used including analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), functional foods, nutraceuticals and physical therapies. A “holistic” approach to management is also emerging, with treatments such as acupuncture and hydrotherapy becoming increasingly available and vets are being encouraged to make environmental assessments and recommendations.
The mainstay of treatment at present tends to revolve around the use of NSAIDs to alleviate pain and moderate the clinical signs associated with the disease. Drugs such as meloxicam (Metacam, Boehringer Ingelheim Vetmedica; Loxicom, Norbrook) and carprofen (Rimadyl, Pfizer; Carprieve, Norbrook) are well established and exert their effects through the inhibition of cyclooxygenase (COX), the enzyme responsible for the conversion of arachidonic acid to prostaglandins and thromboxane.
Isoforms of COX exist, the first of which, COX-1, is considered to be the body’s homoeostatic enzyme with functions including renal perfusion and gastric mucosal protection. COX-2 appears with inflammation and can be induced.
Whilst it is theoretically desirable to selectively inhibit just COX-2, nonetheless there is evidence that the division of function is not black and white. Human patients on COX-2 selective NSAIDs have shown impairment of healing of stomach ulcers.
Nonetheless, in canine patients the preference is towards greater inhibition of COX-2 and recently a new class of NSAIDs has been developed, the Coxibs, which is highly selective in its action. Firocoxib (Previcox, Merial), the first coxib available for dogs, is 380 times more selective for COX-2 than COX-1.
Further debate centres on the effects of NSAIDs on cartilage. The pathological process of OA leads to loss of articular cartilage and hence the resilience and shock-absorbing properties of the joint are compromised.
Whether NSAIDs can play a chondroprotective role is a point of interest and in vitro studies for some products seem to suggest so. Overall though, the potential for side-effects together with the concern that analgesia may lead to overloading of damaged joints, have led to the recommendation to aim for the minimum drug dosage to control clinical signs of the disease.
Recent research, however, questions this approach. It has been demonstrated that “up-regulation” of receptors in response to pain leads to anatomical changes in central pain pathways; not only does the animal become more sensitive to pain, but the intensity of that pain is increased.
This has been termed “central sensitisation” and can lead to the pain becoming difficult to control. Hence, there is an emerging argument for stopping the pain before this change can happen, through using continuous pain management. Work is soon to be published on a new coxib, mavacoxib (Trocoxil, Pfizer) which has this aim.
Traditionally, cats have not received the same focus when it comes to OA, most likely due to their nature in disguising pain and the fact that the clinical signs in this species are more subtle and are commonly mistaken for simple ageing change. However, the disease is increasingly recognised and meloxicam now is licensed for use in the cat.
Nutraceuticals and functional foods
Whilst NSAIDS and other drugs such as prednisolone are targeted at controlling the clinical signs, for example pain, others seek to help to modify the structure of the joint, and so slow progression of the disease.
Popular choices here include combinations of glucosamine and chondroitin sulphate which are thought to provide building blocks of articular cartilage and hence slow down degeneration.
Anecdotally, many owners and vets report good improvements in mobility, although convincing published evidence is still lacking and many orthopaedic experts remain sceptical.
The use of omega-3 fatty acids holds much promise for the field of OA management.
In vitro studies have shown that eicosapentaenoic acid (EPA) blocks the effect of aggrecanase enzymes responsible for the loss of aggrecans and subsequent water-holding ability of cartilage, which has the potential to slow cartilage degradation.
At the same time, the fatty acid is selectively taken up by cell membranes to replace arachidonic acid and hence block the use of this substrate in producing proinflammatory prostaglandins.
Recent clinical studies have shown improvements in both range of movement in OA cases and weight bearing, with a reduction in pain on joint palpation. Hill’s Prescription Diet j/d makes use of this ingredient and a feline version containing docosahexaenoic acid (DHA) and alpha-linolenic (ALA) is available.
Evidence also exists for the use of green-lipped mussel extract in dampening inflammation in joints and this is available in both diet and supplement form.
Hitherto, management of OA has centred on drug and nutrition therapies. Rehabilitation techniques, however, are playing a greater role with more and more vets showing interest in these as an adjunct to, and sometimes replacing, drug therapy. The aim of such techniques for the OA patient is to control pain and maintain mobility and quality of life.
Acupuncture, ultrasound and hydrotherapy are becoming more widely available. Currently though, these services are unregulated in the UK and groups such as Physiovet are calling for tighter controls and to keep these treatments under veterinary supervision.
Massage, TENS and the application of hotcold packs can also be used and owners increasingly look for ways to help their pet at home.
In summary, OA is a progressive and sometimes debilitating disease, but the vet has many tools in his armoury to help maintain mobility and decrease pain. Research into methods to maintain the integrity of cartilage continue and ground-breaking work in areas such as gene therapy might provide us with yet more choice in treatment in the future.