A pernicious triad: Arthritis, obesity and chronic pain

(Shutterstock.com; Getty Images)Arthritis affects at least 20 percent of the pet population,1,2 which can lead to chronic pain, and veterinarians are all too aware of the pet obesity epidemic in the United States. So how do you help these patients, either by slowing the progression of this triad or by tackling these intertwined, yet individual problems?

In a recent Fetch dvm360 session, Tara Edwards, DVM, DACVSMR, CCRT, CVPP, CVMA, said she often sees arthritis patients that are battling not only arthritis but also dealing with the consequences of obesity and, likewise, obese patients on the cusp of developing arthritis.

“There's often this negative cycle of obesity leading to inactivity, leading to weight gain, leading to arthritis. Or flip that around, where we have arthritis leading to inactivity, leading to weight gain, leading to obesity,” she says.

Dr. Edwards explains that both arthritis and obesity limit movement, impact cartilage health, contribute to muscle atrophy, result in weakness and alter biomechanics. As such, both are significant contributors to chronic pain in pets. “Patients are painful before they have altered mobility or lameness,” she says. “So, if we're waiting for lameness, we've missed the boat on early pain management and early arthritis detection.”

Arthritis is a progressive disease, and any change in function is often due to an increase in pain. Among the goals of arthritis patient care are prevention of pain and minimization of disability, she says. This requires earlier identification of arthritis and the implementation of a multimodal arthritis treatment strategy. “Because veterinary patients are nonverbal,” she says, “We need to excel at history taking and physical examinations.”

Since veterinarians rely on clients to be their eyes and ears, it's also essential to educate clients about the clinical signs of arthritis, the progressive nature of the disease and the impact that contributing factors, such as obesity, have on the disease. Education also encourages compliance with your recommended treatments and helps clients understand the need for regular recheck appointments.

Pain begets more pain

When a patient suffers from osteoarthritis, obesity and chronic pain, it has long-term exposure to pain signals. “This can alter the physiology in the spinal cord, decrease pain thresholds, lead to the activation of pain pathways and result in spontaneous electrical activity, exaggerated response to stimuli and altered descending inhibition,” she notes.

The central nervous system (CNS) has its own system of checks and balances, and the descending inhibition pathway is a way the body turns down the intensity of incoming pain signals, Dr. Edwards says. That can change when there is chronic pain. The more pain pathways are utilized, the more efficient the body becomes at transmitting and processing the pain signals. This is called central sensitization or the amplification of pain. Pain begets more pain. These changes in the spinal cord result in hyperalgesia (an exaggerated pain response to a potentially painful stimulus) or perhaps even allodynia (an exaggerated pain response to a nonpainful stimulus). Chronic pain patients may also have expanded receptor fields, which means they have areas that are sensitive well away from the sore joint. Dr. Edwards states that in 20 to 40 percent of human patients with osteoarthritis, their pain is coming from these CNS changes, not the peripheral joints themselves.

“The nervous system has been hijacked,” she says. “We have altered structure and function of the nervous system. Because of that, there's no magic bullet from a treatment perspective. We have to think about multimodal treatment strategies, targeting the underlying neurophysiology and not just symptom control.”

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Acute pain assessments have become a standard of care for trauma, medical and surgical patients. The same is not true for chronic pain, but Dr. Edwards would like to change that. “Ideally, we need to evaluate every patient at every visit for pain. It should be like taking a vital sign,” she says.

It's true that assessing pets for chronic pain is more difficult. The clinical signs are hard to recognize. Pets often don't complain and can even try to hide their discomfort. They slowly adapt to living with the pain and change their activity patterns. Owner observations are needed to help assess pets for chronic pain and changes in mobility. Their feedback can help to identify subtle behavior changes and clues about how the pet is functioning at home. Dr. Edwards recommends three online resources for assessing chronic pain in pets: the Helsinki Chronic Pain Index, the Canine Brief Pain Inventory and the ACVS Canine Orthopedic Index. Keeping track of pain scores at regular recheck appointments will help with evaluating the success of drug treatments and gauge whether a pet's fitness or rehabilitation program is at the appropriate level.

Assessing mobility

Mobility evaluations start with a thorough patient history, followed by observations of the pet as it stands, sits and transitions between different positions and then thorough palpation. Dr. Edwards says an overlooked source of discomfort in veterinary patients is muscle pain or myalgia.

“Myofascial pain is often not recognized, or we're not looking for it. Pets can have primary myofascial pain from a trauma or secondary myalgia, where something else created the muscle pain. Our veterinary patients are often dealing with secondary myalgia,” she says. “They have altered kinetics and changes to posture, weight-bearing and gait. These all can lead to activation of pain pathways.” She says that, in people, myalgia is often described as aching or cramping, and the chronic activation of muscle pain sensors can activate areas in the brain associated with depression.

A retrospective study revealed that 22 percent of cats over 1 year old and 90 percent of cats over 12 years old had radiographic evidence of degenerative joint disease.3 Therefore, for feline patients, history taking is even more important.

“We're looking for very gradual or subtle behavior or lifestyle changes rather than overt lameness,” says Dr. Edwards. “Cats in general are more agile than dogs. Most clients don't take their cats on walks, so they are not observing gait changes. The fact that cats sleep 75 percent of the time can make mobility changes difficult to recognize.”

Dr. Edwards advises asking clients about reduced activity, difficulty jumping, increased grumpiness, changes in sleep patterns, dislike for grooming, avoidance of interaction with people and housemates, appetite fluctuations, weight changes and changes in litterbox habits. She also recommends visiting the International Veterinary Academy of Pain Management website for handouts about common signs of pain to share with clients.

Treatment goals for arthritis patients

Arthritis treatment goals include improving the patient's ability to function and its quality of life. Dr. Edwards states that these can be achieved by controlling pain and inflammation, slowing the progression of arthritis, improving joint function, maintaining muscle strength, preventing injury and promoting physical fitness. She says, “With respect to management, this is a lifelong disease. These patients are going to have this disease for the rest of their lives. So, we have to have good client communication and client support. Management is also dynamic. It needs to change over time because the disease is progressive. It's important for these patients to come in for regular rechecks. One of the main reasons for lack of success for arthritis management is we've failed to adjust our treatments over time.”

Dr. Edwards also states that, as with many areas of practice, managing arthritis becomes more successful with the involvement of the entire veterinary team. And she says it's important for a management plan to be individualized, based on the patient's mobility evaluation. “We need to figure out the disability level to give us the baseline. Otherwise, it's very difficult to determine if our treatment has been successful, or if it's been a failure.”

So, what does Dr. Edwards use as her multimodal toolkit? Head to the next page ...

The multimodal toolkit

In a given management plan, she might include pharmaceuticals, disease-modifying agents to slow arthritis progression, nutrition, physical medicine and rehabilitation, joint injections, regenerative medicine options and surgery, if indicated. “Our goal with multimodal pain management is to maximize our treatment success while minimizing side effects,” she says.

Pharmaceuticals

According to Dr. Edwards, the most commonly used pharmaceuticals in arthritic patients are nonsteroidal anti-inflammatory drugs (NSAIDs), gabapentin and amantadine. NSAIDs are the drugs of choice for initial therapy, since arthritis is an inflammatory disease process. NSAIDs can help increase activity, maintain muscle mass and, because the pet feels like moving again, assist with weight loss.

What about tramadol?

Tramadol is questionable as an appropriate choice for the management of chronic pain patients. Dr. Edwards says, “It's fairly insignificant from a pain management standpoint and it's fairly unreliable in dogs. It has poor oral bioavailability and a very short half-life. Dogs do not produce the ODM metabolite, which is the metabolite with the opioid effect.” Besides the pharmacokinetic issues, tramadol can cause serious side effects including nausea, anorexia, sedation and serotonin syndrome issues. “It's not a benign drug,” Dr. Edwards says. “And it tastes terribly bitter, which can lead to food aversion.”

Determining the lowest effective NSAID dose is ideal, but it may be an unrealistic goal to discontinue the drug in patients with maladaptive pain. “Remember that it takes time to change all of the central and peripheral sensitization that occurs with chronic pain,” says Dr. Edwards. “We know that a longer NSAID course is more beneficial; it's almost cumulative. If we discontinue or taper the drug too soon, we may not see the maximal benefit. Continued daily dosing is much better than intermittent dosing as needed.”

Many osteoarthritis patients benefit from the addition of a second pharmaceutical when an NSAID is no longer sufficient. “Gabapentin is a great choice for chronic and neuropathic pain,” Dr. Edwards says. “It alters the calcium channels involved in excitatory pain synapse formation. It activates descending inhibitory pathways, the body's pathway to turn down the intensity of incoming pain information. It may affect glial cells, which are huge players in neuropathic pain. It modulates pain signals to unwind the windup and resets the pain thermostat.”

She notes that in human patients with chronic pain, gabapentin administration is rarely discontinued. Therefore, she doesn't worry about getting her patients off of gabapentin. She continues it while tapering the NSAIDs.

Another drug she uses is amantadine, an NMDA receptor antagonist, which is in the same category as ketamine. “NMDA receptors play a key role in inducing and maintaining central sensitization. So shutting down those receptors is beneficial,” she says. “Amantadine is not an analgesic by itself, so it's used in conjunction with other pain medications. It quiets the receptors and allows the other medications that are on board to work more effectively.”

With any of these pharmaceuticals, Dr. Edwards waits 10 to 14 days to allow the patient to reach a steady state before changing a drug dose.

Disease-modifying agents

Despite pharmaceuticals targeting inflammation, providing pain relief and modulating neurophysiology, they do not alter the disease progression. As stated earlier, one goal is to slow the progression of arthritis and try to protect the joint cartilage, which is where disease-modifying supplements play a role. The earlier these are administered, the better the chance of modulating cartilage damage.

“Use these products early, while we still have cartilage. You can't turn back the clock with cartilage damage,” Dr. Edwards advises. “These are part of a multimodal plan; never use them as a sole agent or as a replacement for pain-relieving medications.”

Common disease-modifying agents include glucosamine, chondroitin, omega-3 fatty acids, green-lipped muscles, avocado soybean unsaponifiables and injectable chondroprotectants such as polysulfated glycosaminoglycan (Adequan) and pentosan polysulfate sodium (Cartrophen [available in Canada and other countries]).

Nutrition

Weight loss is the single most important factor to help with reducing pain in overweight and arthritic patients. Achieving an ideal body weight is critical for maintaining joint health and slowing the progression of arthritis. Dr. Edwards explains that arthritis is an inflammatory disease by nature and obesity is a source of chronic inflammation. Adipocytes release hormones that have local and systemic effects. Increases in body condition scores are associated with an increase in inflammatory markers, which means that overweight patients are in a constant state of inflammation. Obesity contributes to a pro-inflammatory state, which activates pain sensors, increases pain perception and aggravates joint degeneration by destructive enzymes. Obesity and arthritis exacerbate each other; it is a constant struggle of arthritic patients becoming overweight because of reduced mobility, and overweight patients developing arthritis at faster rates than typical.

Dr. Edwards states that pet owners and, unfortunately, veterinary healthcare teams simply don't recognize obesity in pets. Despite obesity being easily visible, more than 50 percent of dogs and cats are overweight. Dr. Edwards says that veterinarians need to focus on the pets that would benefit the most from early intervention, the ones with a 6 to 7 body score (on a scale of 1-9).

“When talking about obesity and weight control with clients, we need to remove emotion and focus on the health risks of excess weight-that it compromises mobility, compounds arthritis and contributes to the pet's pain.” More importantly, she says, “Obesity affects quality and quantity of life, which impacts the human-animal bond.”

Dr. Edwards recommends using one of the available scoring systems and recording a body condition score (BCS) for every patient at every visit. She says estimating a BCS allows you to determine a pet's ideal body weight, which is necessary to calculate the appropriate calorie intake for the pet. Simply reducing the current volume of food is not ideal for long-term balanced nutrition. It is important to choose a food that is appropriate for weight loss versus one for weight maintenance or obesity prevention. Dr. Edwards says, “OTC diets are for less than five percent weight loss. Otherwise, use prescription diets that are lower calorie and nutrient dense. You don't want to just reduce the volume of normal food. Doing so may just slow metabolism. Use prescription weight-loss diets when you can.”

Dr. Edwards also recommends the use of gram scales to measure feeding portions and encourages the use of food puzzles or games for mental stimulation. Once at an ideal body weight, patients are less likely to regain weight when they continue to be fed the weight-loss diet, adjusted for a caloric intake appropriate for weight maintenance.

Ready to get physical? Head to the next page ...

TLC tips for the clinic and beyond

Giving these patients a little extra TLC in the clinic or at home can go a long way toward patient comfort. Dr. Edwards recommends taking the following steps in your veterinary clinic:

Increase traction on slippery clinic floors

Use mats for orthopedic examinations

Remember sore joints during handling for catheters, nail trims, and with positioning of sedated patients for dentistry and radiographs

Send patients home with “nice feet.” Dr. Edwards takes the time, especially when a patient is anesthetized for another procedure, to trim the nails and trim the hair between the toes to provide more traction for the footpads.

Dr. Edwards also helps her clients make their homes more comfortable for arthritic and obese pets by having them:

Take dogs for controlled and structured leash walks, rather than allowing uncontrolled off-leash activity

Avoid high-impact activities

Adapt the home environment by limiting access to stairs with gates and supplying ramps for access to the car or furniture

Provide comfortable bedding

Elevate feeding dishes

Increase traction on the slippery floors

Use assistive devices, such as slings or carts, as recommended by the veterinarian

Trim nails and the hair between the toes.

According to Dr. Edwards, the overall goal with these patients is to minimize pain while maximizing mobility.

Physical medicine options

“Physical medicine is all about supporting the body as it heals and restoring functional ability,” Dr. Edwards says. She thinks a tailored rehabilitation program can reduce pain and inflammation, improve joint health and mobility, maintain and improve muscle mass, improve proprioception and stimulate overall mental health and physical fitness. Physical medicine options for patients with arthritis and chronic pain include cryotherapy, thermotherapy, laser therapy, acupuncture, land-based treadmills, hydrotherapy and tailored exercise regimens. According to Dr. Edwards, low-intensity exercise can benefit patients by supporting the loss of fat versus muscle, increasing oxygen capacity and energy expenditure, improving joint and muscle function, improving stamina and reducing lameness.

She reminds practitioners, however, “You have to break the pain cycle before you can improve function with physical medicine. Adequate pain management is required for our patients to successfully engage in a rehab or fitness program. We should be assessing pain levels all of the time, at all stages. Any rehab or fitness program should be based on the patient's current limitations and physical fitness. Our goal is to challenge the body over time, based on the goals of treatment.”

Tara Edwards, DVM, DACVSMR, CCRT, CVPP, CVMA, is a certified veterinary pain practitioner and is board-certified in sports medicine and rehabilitaton. She oversees the rehabilitation service at Tri Lake Animal Hospital & Referral Centre in Kelowna, British Columbia, Canada.

References

1. Johnson JA, Austin C, Breuer GJ. Incidence of canine appendicular musculoskeletal disorders in 16 vet teaching hospitals 1980-1989. Vet Comp Orthopedics Traumatolog 1994(7):56-69.

2. Johnson SA. Osteoarthritis. Joint anatomy, physiology, and pathobiology. Vet Clin North Am Small Anim Pract 27(4):1997;699-723.

3. 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):628-632.