Osteoarthritis (OA) has long been recognized as an important source of chronic pain in people, with over 70 percent age 65 or older showing radiographic evidence of it.
OA has emerged as the leading cause of chronic pain in pets. About 20 percent of dogs, independent of age, suffer the effects of osteoarthritis. Recent data suggests that 100 percent of cats 10 or older exhibit radiographic signs consistent with osteoarthritis.
The veterinary profession does not face any other cause of morbidity as widespread as this. Because the incidence is so high, veterinary health care teams are obligated to expand our understanding of how best to manage patients suffering from OA.
One of the most important developments in chronic pain management has been the recognition of the complex nature of the nervous system’s processing of pain. Pain involves many receptors and neurotransmitters and many different mechanisms and actions.
The malleability, or plasticity, of the nervous system in the face of pain provides the opportunity for both central and peripheral sensitization, the result of which is often debilitating and difficult-to-reat pain. In animal patients who suffer from chronic OA pain, traditional monotherapy—the use of a single agent such as a NSAID—often fails or at least provides a less-than-optimal outcome. To achieve optimal results, we must think past the NSAID.
Get Weight Under Control
Obesity in pets is now an epidemic. For the obese pet suffering from OA, weight loss alone may significantly improve function and comfort. It is critical to utilize a nutritional product specifically formulated for weight loss. OTC diets typically cannot do the job.
Also, recent nutrogenomics data in dogs is fairly compelling in favor of the “functional food” concept, whereby we can down-regulate “obesity genes” and up-regulate “lean genes.”
In addition to weight loss, we must focus on breaking the cycle of chronic pain, which is a manifestation of maladaptive pain influenced by several important mechanisms in the nervous system. Thus our pharmacologic approach must attack pain from multiple directions.
We utilize NSAIDs for their anti-inflammatory and analgesic effects. In addition, we can use amantadine to target NMDA receptors in the dorsal horn of the spinal cord as an effective adjunct to NSAIDs (Lascelles, et al). Another useful target is the alpha-2 ligand on the calcium channel of the neurons in the dorsal horn. Gabapentin affects this ligand to alter calcium permeability within the cell membrane, altering the transmission and modulation of pain signals.
Finally, the tricyclic antidepressants offer yet another target of our multimodal drug therapy in our quest to quell pain. These agents work together synergistically better than any one works on its own. And they are all compatible.
While we generally need to rely on pharmacology at some level with these patients, managing OA mandates incorporating additional, non-drug strategies for optimal outcomes. These include disease modifying agents, of which injectable poly-sulfated glycosaminoglycans (PSGAGs) are one. PSGAGs give us the opportunity to provide the body with the building blocks of cartilage, assisting the body in repairing its tissues.
Likewise, nutraceuticals are gaining in popularity. The scientific evidence guides us to incorporate high levels of omega-3 fatty acids—specifically EPA and DHA—into the daily nutritional profile. Therapeutic canine and feline joint-support foods, backed by solid clinical research, provide anti-inflammatory levels of bioavailable omega-3 fatty acids.
If a pet needs to eat a different therapeutic nutritional profile than that designed for joint support, one company produces a cod liver oil preparation that exceeds international pharmaceutical standards and provides a high enough concentration of EPA and DHA to make a positive difference for OA patients.
Another important nutraceutical supported by scientific evidence is the molecule microlactin, which has been demonstrated to reduce inflammation by inhibiting neutrophil migration via blocking cytokines. Finally, the avocado and soybean unsaponifiables (ASU), combined with low molecular weight chondroitin, have been demonstrated to have a positive effect in animals with OA.
The bad news about the nutraceuticals and nutritional supplements that we use to manage OA and its related pain is that we have no evidence to support the idea that we can prevent the onset of OA simply by incorporating these products.
That said, if we are taking care of a pet that has congenital or conformational issues that alter biomechanics away from normal, that pet is at high risk for developing OA over time. In that case, it’s common sense to think about putting joint support into play early to at least delay the onset and progression of the inevitable.
The next addition to the OA management plan should be physical medicine. This wide-open term incorporates everything from acupuncture and chiropractic through full-service. Therapeutic laser can have a very positive effect on pain-filled OA patients. Heat therapy, cold therapy, medical massage techniques and therapeutic exercises can be taught to clients to get them active in helping their pets become more comfortable and functional.
Modifying the home environment can make a huge impact on a pet’s comfort. Raised food and water dishes, vehicle loading ramps, non-skid floor coverings and carpeted pet steps for furniture and bed access are simple ways to give effective assistance.
Finally, don’t forget the importance of regular reassessments and revisions of the pain management strategy. Early in implementing a multimodal approach, rechecks should happen fairly frequently, usually every two to three weeks. As patients become more comfortable and active, the interval between re-evaluations can be lengthened somewhat. It is quite reasonable to see these patients at least quarterly once they are stable.
Little in veterinary medicine is as rewarding as restoring a dog or cat in pain to a previous level of comfort, function and mobility. It is a bit addictive, in fact. You may find yourself looking at your older patients through new eyes, seeking and finding pain just waiting to be treated.
What About Cats?
Cats with osteoarthritis pose unique challenges to clients and veterinary health care teams. The most important challenge is that cats, as predators by nature, are generally reluctant to demonstrate any disability. Even though domestic cats no longer rely on hunting skills, their nature is to behave as though they do.
The best strategy for identifying chronic pain in cats is to be vigilant in conversations and history-taking with the client. The most common signal to practitioners that a cat is in pain is a change in its everyday behaviors. Commonly reported changes include:
• Reluctance or refusal to jump onto surfaces or structures previously frequented, such as windowsills, furniture and cat trees.
• Reluctance or refusal to move up and down stairs in a multistory home.
• Inappropriate elimination on one level of the home when the litter pan is on a different level.
• Reluctance to be held, handled or petted, particularly if one area of the body appears to be off limits.
• “Missing” the litter pan—either difficulty getting over a high-sided pan or an inability to squat during urination, thus urinating over the edge.
If the history is consistent with a diagnosis of chronic pain, then additional diagnostics should be conducted. These include radiographs of the hips and spine and a metabolic profile with a microalbuminuria test on urine and blood pressure. This allows for treatment of the whole cat, ensuring we do not overlook any co-morbidities.
The treatment plan for a cat with OA is remarkably similar to that for dogs. Multimodal management remains our best strategy, and we can, in general, utilize all the same tools as in dogs. Indoor cats have the highest risk and incidence of obesity, so weight loss and management remains a cornerstone of managing feline OA.
Likewise, NSAIDs may play a role, at least for a time, in reducing the OA inflammation while other strategies have a chance to take effect. The American Association of Feline Practitioners and the International Society of Feline Medicine have jointly published consensus guidelines on the use of NSAIDs in cats. (See the July 2010 issue of the Journal of Feline Medicine and Surgery.)
At the Downing Center for Animal Pain Management we rarely use NSAIDs in cats. Instead we rely on adjunctive medications such as amantadine and gabapentin, nutrition, PSGAGs, microlactin, omega-3 fatty acids and physical medicine like acupuncture, chiropractic, physiotherapy and hydrotherapy. —R.D.
Two important resources for the veterinary professional are the AAHA/AAFP Pain Management Guidelines for Dogs and Cats and membership in the International Veterinary Academy of Pain Management. IVAPM membership—visit IVAPM.org—is open to veterinarians, veterinary technicians and any other health professionals who help treat pain in animals.
Robin Downing, DVM, CVA, CVCP (IVCA), CPE (ASPE), CCRP, Dipl. AAPM, owns Windsor Veterinary Clinic and the Downing Center for Animal Pain Management in Windsor, Colo.