By Brennen McKenzie, MA, MSc, VMD, cVMA

Osteoarthritis (OA) is among the most common age-related conditions in cats. Research suggests 30 to 90 percent of older cats shows signs of OA, and many experience pain and dysfunction.^1,2

It is challenging to assess pain in cats, and owners often do not appreciate the impact chronic pain has on their feline companions. It is also challenging to measure the impact of analgesic therapies on cats. Caregiver placebo effects are a significant issue in the treatment of feline pain, and this further complicates OA management in this species.³

Fortunately, there are tools and techniques for assessing OA pain, and a number of therapies that can effectively and safely improve comfort in cats with OA.

Assessing arthritis pain

Many owners expect cats to manifest pain through vocalization, but this is uncommon except for sudden acute pain. Chronic pain more often manifests as changes in behavior, which may be subtle. Decreased activity in general, particularly decreases in running, jumping, climbing, and more vigorous types of activity, can be a sign of OA.

Undergrooming and matted hair, especially in the hindquarters, may also indicate OA pain. Additionally, cats may exhibit changes in elimination, such as crying when eliminating, or inappropriate elimination, due to difficulty getting in and out of a litterbox or negative associations with the box caused by past pain.^1,2,4,5

There are several pain-assessment tools available for cats with OA, including:

• Feline Musculoskeletal Pain Index (FMPI)—North Carolina State University^6-9
• Client-Specific Outcome Measures (CSOM)—North Carolina State University¹⁰
• Montreal Instrument for Cat Arthritis Testing for use by caretaker (MI-CAT(C))^11,12
• Montreal Instrument for Cat Arthritis Testing for use by veterinarian (MI-CAT(V)) ¹³

These are especially important in assessing the impact of analgesic therapies. Studies have demonstrated cats with OA getting placebos in clinical studies are often reported to be improved, despite receiving no active therapy. There are many factors that can contribute to such placebo effects, but the tendency of owners and veterinarians to see the improvement they expect and hope for after initiation of a treatment can lead to the false impression of efficacy.¹⁴

There are also instruments for assessing quality of life in cats:

• Health-related Quality-of-Life instrument (HRQL)—Vetmetrica^15,16
• Cat Health and Wellbeing (CHEW)¹⁷
• Feline QoL measure¹⁸

These have a role in evaluating treatment of OA because controlling the associated pain and disability should manifest as improvement in overall quality of life.

Analgesic options for cats with arthritis

The most commonly used and best-studied analgesic options for cats with OA are pharmaceutical treatments. There is significant variability among these, however, in the strength of evidence for safety and efficacy. In addition, there are supplements, dietary and environmental interventions, and a plethora of physical medicine therapies, most of which have little reliable scientific evidence to support their use.^1,2,4,5

Unfortunately, the preferences among veterinarians for analgesic therapies in cats with OA do not align well with the strength of supporting evidence. One survey¹⁹ indicated the following prescribing practices among respondents:

These preferences varied with factors other than strength of evidence. For example, veterinarians with less than one year in practice were least likely to prescribe any therapy for cats with OA, which suggests unfamiliarity or lack of confidence with available options may lead to undertreatment.

In contrast, older veterinarians, particularly those with more than 20 years in practice, were more likely to prescribe glucocorticoids, a therapy rarely appropriate in terms of risk/benefit balance given the alternatives available.

The most commonly prescribed medicine was gabapentin, which lacks strong evidence of efficacy for OA in cats.^5,20 Meloxicam, in contrast, has extensive evidence supporting safety and efficacy for this condition, yet is less favored, at least in the United States, likely due to a warning regarding its use issued in 2011 by the FDA.^6,21-23

Despite this, meloxicam is licensed for chronic use in cats and is widely employed by veterinarians in other countries.

The following brief review is not intended as an exhaustive analysis of OA treatment options, but as a brief summary of the evidence currently available.

NSAIDs

These are by far the most demonstrably effective medicines currently available for OA pain in cats. The use of nonsteroidal anti-inflammatory drugs (NSAIDs) is supported by such organizations as the American Academy of Feline Practitioners (AAFP) and the World Small Animal Veterinary Association (WSAVA) because there is strong evidence for both efficacy and safety.^5,22-24

There are, of course, also potential risks with NSAIDs, as with any effective medicine. However, even in cats with established chronic kidney disease (CKD), meloxicam has proven safe for long-term use with appropriate case selection and monitoring.

Robenacoxib is also used for OA, and while there is less research evidence and clinical experience supporting its use, its pharmacologic profile suggests potential advantages over meloxicam.^25,26 Further investigation is needed to determine which drug, if either, is clinically superior. It is unfortunate so many cats undoubtedly suffer unnecessarily from chronic pain due to excessive anxiety on the part of veterinarians and owners about the safety of NSAIDs.

• Gabapentin. There is a plausible rationale for the use of gabapentin to treat chronic and acute pain in cats. Apart from sedation, there are few reports of adverse effects. Unfortunately, there is only weak evidence it is effective for management of OA pain.⁵

The experience of tramadol in dogs, a wildly popular drug that turned out not to be effective, should inspire caution about relying on analgesics with limited evidence of effectiveness.²⁷

• Tramadol. There is somewhat more reason to expect tramadol might be effective in cats with OA than it is in dogs. The preclinical evidence is encouraging, and small trials with some limitations have so far shown positive effects on pain in cats.^27-29

It remains to be seen, however, if this is sufficiently safe and effective to be a reliable mainstay of feline OA management. Tramadol is also bitter, and it can be difficult to provide in a form acceptable to many cats.

• Opioids. Surveys suggest using opioids for chronic musculoskeletal pain in cats is relatively common. It is likely transmucosal buprenorphine makes up most of this opioid prescribing given the serious concerns about prescribing opioids for injection.

Most of the research on opioid analgesia in cats involves acute or surgical pain, and there is a lack of evidence concerning the relative risks and benefits of using this class of drug for long-term management of feline OA pain.^5,22,30

• Other pharmaceuticals. There are many other drugs sometime used to manage chronic OA pain in cats, including glucocorticoids, amantadine, maropitant, ketamine, selective serotonin reuptake inhibitors, cannabinoids, and more.^5,22,31,32

There is a lack of compelling clinical research evidence for most of these, and their use is based mostly on pathophysiologic rationales and clinical experience. The limited evidence of efficacy for most of these makes prescribing them essentially experimental trial and error, which should be resorted to only after more validated therapies have been considered.

There is a promising new option that has been recently approved for treatment of OA pain in cats; an anti-nerve growth factor monoclonal antibody called frunevetmab.³³ The studies supporting licensure show good safety and efficacy, though these will need to be reproduced and expanded in real-world patient populations. If this drug fulfills its promise, it could be a dramatic step forward in the management of feline OA.

• Nutraceuticals. There is a vast array of nutraceutical products available for use in cats with OA, including glucosamine and chondroitin, fish oils, polysulfated glycosoaminoglycans, and many others. Generally speaking, the evidence for all of these is poor. Preclinical evidence, small clinical studies with methodological limitations, and, of course, mountains of anecdotes are cited to support the safety and efficacy of therapies in this group.^34-38

My approach when discussing these products with clients is to emphasize the uncertainty around both efficacy and safety, as well as the quality control problems associated with unregulated supplements. Therapy should always focus on those treatments with the strongest evidence and then proceed down the evidence pyramid to those therapies for which there is less-compelling data.

This does not mean we should not use such products when we are unable to achieve good control of pain without unacceptable side-effects using better-substantiated remedies. However, the limited evidence for these options imposes on us an obligation to be clear and explicit with clients about the relevant uncertainties and not to suppose our personal clinical experience is more reliable than it actually is.

Nonpharmaceutical therapies

Many interventions other than drugs are employed in cats with arthritis, including physical therapy, massage, acupuncture, chiropractic, cold laser, and others. Once again, there is a lack of strong clinical research evidence supporting most of these, though this does little to diminish confidence in these treatments based on theoretical rationales or personal experience.³⁶

I recommend employing such methods only when better supported treatments have been tried and with full disclosure to cat owners of the limitations and uncertainties in the scientific evidence for these modalities.

Bottom line

Osteoarthritis is a common cause of chronic pain in cats. It can be difficult to identify and measure pain in cats, but there are tools that can help, and both veterinarians and clients should be encouraged to use these.

There are many analgesic options for cats with OA, ranging from weight loss and environmental modification to pharmaceuticals, supplements, and physical medicine modalities. Apart from a few drugs, most of these are supported by limited and often unreliable evidence, and the caregiver placebo effect hampers our ability to accurately assess the value of OA treatments for cats.

Preference should be given to the best-validated interventions first, and explicit discussions should be had with owners about the risks, benefits, and evidentiary uncertainties associated with any treatment offered so they can make fully informed decisions about how to help their feline companions.

Brennen McKenzie, MA, MSc, VMD, cVMA, discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians. Columnists' opinions do not necessarily reflect those of Veterinary Practice News.

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