Joint disease in cats: Assume the worst and treat for the best

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What's the first thing that comes to mind when you see a senior cat? For Kelly St. Denis, DVM, DABVP (feline practice), owner of Charing Cross Cat Clinic in Brantford, Ontario, it's pain. That's because according to research, senior cats with degenerative joint disease (DJD) are the majority.

Dr. St. Denis cites a 2002 study¹ that found radiographic evidence of DJD in 90% of cats greater than 12 years of age, as well as a 2010 study² that found radiographic evidence of DJD in 92% of cats between 6 months and 20 years of age with equal frequency in all age groups. “In the second study, age was the only variable consistently associated with DJD,” she explains. “And for each one-year increase in a cat's age, the expected total DJD score increased more than 13%.”

While radiographic changes don't always correlate with pain, Dr. St. Denis would much rather assume a cat is painful and be wrong than vice versa-especially since these patients are notoriously skilled at concealing signs of suffering. This assumption means her senior feline exams start slow and as hands-off as possible. “Sometimes clients want to push, pull, drag, shake or dump their cat out of the carrier because they don't want to take up too much of my time,” says Dr. St. Denis. “I help them take a step back, open the carrier on the floor and give the cat a chance to come out on its own.”

From here, the work of diagnosing DJD begins. Drawing on both published research and her 20 years of clinical practice experience, Dr. St. Denis explained how she follows up on her assumptions during a session sponsored by PRN Pharmacal at a recent Fetch dvm360 conference.

DJD defined

Degenerative joint disease (DJD) is an umbrella term that includes osteoarthritis (OA), spondylosis deformans of the intervertebral disc, isolated degenerative lesions, traumatic arthritis and non-OA-related degenerative soft tissue mineralization within a joint. OA and spondylosis deformans are the most common causes of DJD in cats.

A diagnostic puzzle

Dr. St. Denis likens DJD's diagnostic components to puzzle pieces. Sometimes they fit together nicely, and sometimes they don't and you're still left with your research-based assumptions.

Medical history. Getting a helpful history from your clients can be difficult, says Dr. St. Denis, and it's not just because cats are so good at masking their pain. Unlike dog owners, cat owners are less likely to interact physically with their pets on a regular basis, and cats' rigorous sleep schedule can make it difficult for their owners to observe their activity. This difficulty is further compounded by cat owners being uneducated about what to watch for and perhaps even blinded to changes by a fear of facing the aging of their beloved companion.

According to Dr. St. Denis, equipping your clients to become allies in DJD detection can help you get to a diagnosis sooner, and that client will be more likely to see the need for treatment. “I most often hear from cat owners that their cat is simply getting old, as if that's some sort of excuse for why the cat isn't doing anything anymore,” she says. “We have to adjust their interpretation of that slowing down.”

Common signs associated with DJD

> Reduced activity

> Decreased grooming

> Hair loss over affected joints (likely due to increased grooming)

> Irritability and aggression

> Litter box issues

> Constipation

> Odd sleeping positions (e.g. with limbs sticking out)

> Increased sleeping

> Sudden dislike of brushing, petting, etc.

> Body weight and appetite changes

> Lameness

Dr. St. Denis notes that it can be helpful to pry when it comes to litter box issues, because cat owners often adjust to a new “normal” without thinking anything about it. New behaviors, such as missing the box with urine, can create unconscious habits, like laying down pee pads, that ignore the underlying issue-such as pain.

In addition to discussing the common signs associated with DJD (see sidebar), Dr. St. Denis recommends training clients to use the Feline Musculoskeletal Pain Index, a clinically validated questionnaire for diagnosing and monitoring pain stemming from degenerative joint disorders.

Physical exam. As mentioned earlier, Dr. St. Denis starts physical exams by setting the carrier on the floor and letting the cat come out on its own. In addition to being sensitive to potential pain, this approach gives you an opportunity to watch the cat move around the room. “If it's a patient you're familiar with, you're going to notice if there are changes in the way that cat moves, and you might notice changes in weight, behavior and response to handling as well,” she says.

Body and muscle condition scoring are key parts of the physical exam and client education. Dr. St. Denis has the World Small Animal Veterinary Association's charts on her exam room walls and gets clients to do the scoring with her during the exam.

Orthopedic exam. If you're concerned about identifying painful DJD, you'll need to include an orthopedic exam to look for changes in the joints of both the appendicular and axillary skeleton, says Dr. St. Denis. “You're going to be looking for changes in muscle atrophy, restricted range of motion, crepitus, joint effusion and periarticular thickening,” she explains. “You'll also need to run your hands along the vertebrae to check for spinal pain.”

Radiography. Radiographs can be frustrating because radiographically normal joints can be pathologically and clinically affected, and those that look affected can be pain-free, says Dr. St. Denis.³ Nevertheless, she notes that radiographs can be helpful in discerning which joints are affected and how severe they are. They can also aid in identifying surgical candidates. “But when you're doing this, don't forget to use pain medication, sedation and anesthesia because this hurts,” she urges. “To get a proper view of any of these joints, cats have to stretch and bend and hold still-all things they don't like.”

At this point, if the diagnostic puzzle pieces aren't fitting together but you still have a hunch the cat is experiencing musculoskeletal pain due to its age, you can also assess the cat's response to therapeutics.

Treating multiple pain pathways

According to Dr. St. Denis, the three main goals of treatment are to reduce pain and inflammation, improve joint function and mobility, and slow the disease process so the cat has a better quality of life for longer, and you have many modalities at your disposal, including nutrition, nutraceuticals, analgesia and environmental modifications.

Nutrition. “First and foremost,” says Dr. St. Denis, “if the cat is overweight, we definitely want to work at a controlled weight loss program because that will help with its overall demeanor, activity levels and how it's feeling. We know that fat cells release proinflammatory mediators, and we don't need to egg on inflammation.”

When selecting a therapeutic diet, you'll need to consider comorbidities, as Dr. St. Denis notes that cats like to have more than one medical problem at a time (e.g. kidney problems and diabetes). “If they're overall healthy senior cats, something like the Royal Canin Senior Consult is a good food because it has omega-3 fatty acids, green-lipped mussels and a number of other features in it that are helpful with joint health,” she says. Other recommended diets include Royal Canin Mobility Support and Hill's k/d + mobility.

Nutraceuticals. While there are a lot of nutraceuticals available, cat-specific data on these products is lacking. However, Dr. St. Denis notes that data from canine studies can be extrapolated.^4,5

Microlactin (Duralactin-VPL).Microlactin is a protein concentrate from the milk of hyperimmunized cows. “It's been shown to reduce inflammation throughout the body,” says Dr. St. Denis. “It's ideal for long-term use, has minimal side effects and is suitable for high-risk animals like cats with chronic kidney disease (CKD).”

Chondroprotectants. Injectable chondroprotectants like polysulfated glycosaminoglycan (Adequan) and pentosan polysulfate sodium (Cartrophen) aren't licensed for use in cats, but Dr. St. Denis has seen improvements with their use in her practice. “I've had clients notice changes in their cat's mobility at home, and they'll notice when the interval is up between injections,” she explains. One perk of chondroprotectants is that you can teach your clients to administer the injections on their own.

Analgesia. On the topic of analgesia, Dr. St. Denis begins with some words of caution. “Many products available are not licensed for use in DJD in cats in the United States,” she explains. “Several of these products are licensed elsewhere in the world for this purpose but have not yet obtained FDA approval. You should be very aware of licensing restrictions on these products and utilize them carefully.”

Multimodal: the name of the pain (relief) game

“Pain from affected tissues can travel to the spinal cord and brain via several pathways,” says Dr. St. Denis. “Many mechanisms are involved, including inflammatory, nociceptive, neuropathic and central hyperalgesia.” Hence the need for a multimodal approach.

When explaining this to clients, Dr. St. Denis turns to a transportation analogy. “I talk to them about the 401, which is a major highway that goes into Toronto,” she says. “It has six lanes in each direction. If you block one lane to the highway, you're going to slow traffic down a little bit. But what we want to do is block multiple lanes.”

Acute pain. Some patients may need you to first address acute pain before you can get to the chronic problems, says Dr. St. Denis. “If I admit such a patient, I might start it on intravenous fluids with a ketamine constant rate infusion as an [N-methyl-D-aspartate (NMDA)] receptor blocker,” she explains. “I will probably start [nonsteroidal anti-inflammatory drugs (NSAIDs)], and I will definitely have it on a narcotic. Buprenorphine happens to be one of my favorite drugs, but I do use gabapentin as well.”

Acute analgesic dosing

Dr. St. Denis uses the following dosages for feline patients with acute pain:

• Buprenorphine: 0.02-0.04 mg/kg intravenously or intramuscularly at the time of the appointment, or transmucosally 60 to 90 minutes before handling
• Gabapentin: 10-20 mg/kg by mouth 60 to 90 minutes before handling.

Dr. St. Denis starts these cats at fairly high dosages (see sidebar)-dosages that also work if you're having the cat come in for an appointment. “If you have cats that are difficult,” she says, “gabapentin provides a sedation effect in addition to analgesia, and a lot of the cats that are difficult in your practice are actually painful, so you're addressing the root issue.”

Chronic pain. Long-term analgesia will be necessary for cats diagnosed with or presumed to have DJD-related pain, says Dr. St. Denis. While there are several options to choose from, she can help you strike two from the list: buprenorphine and tramadol. “Buprenorphine isn't practical or licensed for long-term use for cats with DJD,” she explains. “And clients have such a hard time administering tramadol to their cats due to its terrible taste that I don't really use it. Plus, it has significant side effects. For long-term use, we're better off considering analgesics that can be administered orally at home, have fewer side effects and are not scheduled drugs.”

• Gabapentin, which acts in the dorsal horn of the spinal cord-inhibiting voltage-gated calcium channels-can be useful for both acute and chronic pain, says Dr. St. Denis. And while the drug is off-label for use in cats, she notes a 2018 study in which gabapentin was associated with improved owner-identified impaired activities in OA-affected cats.⁶

Gabapentin can cause sedation and an altered or ataxic gait, though these effects wear off after two to four weeks of use. “I let clients know to call us if they become concerned by these side effects, because we'll help them dial the dose back and then we'll move it back up slowly,” says Dr. St. Denis. “We don't want clients abruptly discontinuing gabapentin, because the cat can have a higher level of pain in response.”

She starts with anywhere from 6-15 mg/kg. “It's very tailored to the patient,” Dr. St. Denis explains. “Cats with CKD or muscle wasting, we start low. A healthier, more robust cat may require higher dosages.”

• NSAIDs like meloxicam are licensed restrictively in the United States, but Dr. St. Denis says they are still options. “We have a lot of great studies showing safety-that have looked at the effects of long-term dosing on renal function in aged cats-so we know they don't cause any huge problems,” she says.^7-9 “Still, I'll have a conversation with the owner of a cat with [IRIS (International Renal Interest Society)] stage 3 kidney disease before putting it on an NSAID and say, ‘If we want this cat to be comfortable, it may not live as long but may have a better quality of life.' I talk to the client about the risks and rewards and let them make a decision about how they want to proceed.”

In January, robenacoxib (Onsior-Elanco) received new licensing in Canada for long-term use in cats with chronic musculoskeletal pain, so Dr. St. Denis is starting to use it more with her DJD patients. However, it's still licensed only for postoperative pain in the United States.

Environment. One last key component of Dr. St. Denis' multimodal approach to pain management involves considering the cat's environment. This includes keeping it active (e.g. food puzzles and playtime with the owner) and improving its access to resources (e.g. providing a low-walled litterbox on every floor of the cat's home and installing nightlights for cats with diminishing vision).

When you're unsure, go ahead and assume

Feline DJD is more common than we think, says Dr. St. Denis. “The pain is real, but the nature of cats as a prey species means this pain is often silent,” she says. “Once we successfully identify DJD in our feline patients, utilization of a multimodal approach is the best option for success. And if you simply think it could be painful, assume it is because the cat's not going to tell you.”

Sarah Mouton Dowdy, a former associate content specialist for dvm360.com, is a freelance writer and editor in Kansas City, Missouri.

References

1. Hardie EM, Roe SC, Martin FR. Radiographic evidence of degenerative joint disease in geriatric cats: 100 cases (1994-1997). J Am Vet Med Assoc 2002;220(5):628-632.

2. Lascelles BD, Henry JB 3rd, Brown J, et al. Cross-sectional study of the prevalence of radiographic degenerative joint disease in domesticated cats. Vet Surg 2010;39(5):535-544.

3. Bennett D, Zainal Ariffin SM, Johnston P. Osteoarthritis in the cat: how common is it and how easy to recognize? J Feline Med Surg 2012;14(1);65-75.

4. Vandeweerd JM, Coisnon C, Clegg P, et al. Systematic review of efficacy of nutraceuticals to alleviate clinical signs of osteoarthritis. J Vet Intern Med 2012;26(3):448-456.

5. Gingerich DA, Strobel JD. Use of client-specific outcome measures to assess treatment effects in geriatric, arthritic dogs: controlled clinical evaluation of a nutraceutical. Vet Ther 2003;4(1):56-66.

6. Guedes AGP, Meadows JS, Pypendop BH, et al. Assessment of the effects of gabapentin on activity levels and owner-perceived mobility impairment and quality of life in osteoarthritic geriatric cats. J Am Vet Med Assoc 2018;253(5):579-585.

7. Guillot M, Moreau M, Heit M, et al. Characterization of osteoarthritis in cats and meloxicam efficacy using objective chronic pain evaluation tools. Vet J 2013;196(3):360-367.

8. Gowan RA, Lingard AE, Johnston L, et al. Retrospective case-control study of the effects of long-term dosing with meloxicam on renal function in aged cats with degenerative joint disease. J Feline Med Surg 2011;13(10):752-761.

9. Gowan RA, Baral RM, Lingard AE, et al. A retrospective analysis of the effects of meloxicam on the longevity of aged cats with and without overt chronic kidney disease. J Feline Med Surg 2012;14(12):876-881.