Feline Chronic Pain

The need to recognize and treat chronic pain in cats has received great attention in recent years. Margie Scherk, DVM, DABVP (Feline Practice), discussed the causes and management of feline chronic pain at the 2018 WVC Conference in Las Vegas, Nevada.

Cats often hide their pain, Dr. Scherk noted, so identifying its potential causes may require extrapolation from our own experiences. “If it might hurt you,” she said, “assume it hurts cats.”

TYPES OF PAIN


Pain Categories


Pain can be categorized broadly as nociceptive, inflammatory, and neuropathic. Nociceptive pain is caused by tissue damage such as traumatic injuries, surgical incisions, and burns. Neuropathic pain is related to nervous system lesions or dysfunction; a classic example is phantom limb pain after amputation. Many other conditions can also cause neuropathic pain.¹ Inflammatory pain results from activation of the nociceptive pain pathway by a host of mediators released at the site of tissue inflammation.

Acute Versus Chronic Pain

Acute pain is typically caused by tissue injury. It is self-limiting and results in behavior changes that minimize damage to an animal’s body; this serves a beneficial biological purpose. Chronic pain is often related to inflammation, ongoing nociceptive stimulation, or neuropathic pain; continues longer than expected for a disease process; and adversely affects physical and, at least in humans, psychological health.¹

Acute and chronic pain are clinically different. Treatment of acute pain focuses on removing the source of pain and blocking pain transmission, whereas management of chronic pain focuses on improving the patient’s quality of life, typically by employing more than 1 treatment modality (eg, medication plus environmental modification).¹

These 2 types of pain also overlap. Uncontrolled acute pain can become chronic neuropathic pain, and patients with chronic pain can experience acute episodes of breakthrough pain. Prolonged or repeated pain sensitizes peripheral and central nociceptors, resulting in hyperalgesia, which is an exaggerated response to a painful stimulus, and allodynia, which is a pain response to a normally nonpainful stimulus.¹

To prevent acute pain from becoming chronic, Dr. Scherk said, provide preemptive analgesia and continue to provide analgesia for a sufficient length of time. For surgical procedures, for example, administer analgesics in advance and continue them throughout the healing process until pain transmission has subsided.

SIGNS OF PAIN

Because cats are secretive about their pain, owners may not recognize the signs in their pet. Dr. Scherk recommended asking owners specific questions about potential signs of pain, including a personality change, reduced interaction with the family, decreased activity level, aggression, alteration in sleeping pattern, elimination outside the litter box, reluctance to jump up or down, and inappetence.

In addition, physical examination may reveal a poor haircoat, from reduced grooming, or a defensive reaction to being handled or touched. Dr. Scherk noted that fear and pain may produce similar signs in the clinic. Diagnostic imaging can be helpful.

Response to a treatment trial also can identify pain in cats, Dr. Scherk said. “It’s never wrong to do test doses of analgesia,” she added. A return to normal behavior during analgesic therapy indicates the presence of chronic pain.

The Feline Musculoskeletal Pain Index,² a questionnaire developed at North Carolina State University
to help veterinarians and cat owners identify musculoskeletal pain, may also be useful for nonmusculoskeletal pain, Dr. Scherk said. She suggested that practitioners refer to the 2015 American Animal Hospital Association/American Association of Feline Practitioners (AAFP) pain management guidelines for more information on recognizing and managing pain.³

CAUSES OF CHRONIC PAIN IN CATS

Neuropathic Pain

“Anything can become neuropathic pain,” Dr. Scherk emphasized. And any uncontrolled pain can result in hyperalgesia or allodynia. Amputation, including onychectomy, and insufficiently treated surgical pain lead to neuropathic pain. Other causes are nerve compression (by a tumor, for example), diabetic neuropathy, and posttraumatic neuralgia. Idiopathic cystitis probably has a neuropathic component, she added. Repeated biting or scratching at the same area of the body, spontaneous crying, and an adverse reaction to touch may indicate neuropathic pain.

Degenerative Joint Disease

Degenerative joint disease is very common in older cats but occurs in cats of all ages, Dr. Scherk said. And unlike dogs, cats with degenerative joint disease are not usually lame. The signs in cats are often subtle, and owners may mistake them for normal aging changes.

Other Causes

Bacterial cystitis, sterile (idiopathic) cystitis, and pyelonephritis are all inflammatory and painful, Dr. Scherk said. Additional causes, which may elicit no or only subtle clinical signs, include oral conditions such as periodontal disease, stomatitis, oral tumors, and feline orofacial pain syndrome, a likely neuropathic condition that is seen most often in Burmese cats and causes licking and chewing movements and sometimes tongue mutilation. She also mentioned that dehydration causes headaches in people, so it may well cause similar pain in cats.

Dr. Scherk pointed out that common hospital procedures are uncomfortable for cats with chronic conditions such as osteoarthritis (OA). Palpation, restraint, extending a leg for venipuncture or catheterization, and positioning for radiographs all can cause pain.

TREATING CHRONIC PAIN

Analgesic treatment should begin early, Dr. Scherk said. She emphasized that analgesia should be preemptive, multimodal, and of sufficient duration. Patients with chronic pain should be reassessed regularly because pain responses and treatment needs change over time. The underlying cause of pain should also be treated, if possible.

Dr. Scherk especially stressed the need for multimodal analgesia to prevent and treat chronic pain. Multimodal analgesia is safer than single-agent treatment because it allows for lower drug doses, she said. “The more points of the pain pathway that you hit, the better analgesia you’ll provide,” she said. Effectively blocking pain transmission with multimodal analgesia also reduces the risk that a patient will develop neuropathic pain.

Preemptive Analgesia

Adequate management of perioperative pain can prevent neuropathic pain, Dr. Scherk said. Local anesthetics and N-methyl-D-aspartate (NMDA) receptor antagonists, such as ketamine, are among the drugs used to block pain transmission.

Nonsteroidal Anti-Inflammatory Agents

Nonsteroidal anti-inflammatory drugs (NSAIDs) are more effective than opioids or steroids for managing OA pain, Dr. Scherk said. “NSAIDs are indicated for acute and chronic pain,” she added. Although NSAIDs are associated with serious adverse effects in cats, they can be administered safely if proper precautions are taken, she said.

The only NSAID currently approved in any country for long-term use in cats is meloxicam. In the United States, meloxicam is labeled for cats as a single subcutaneous injection to control postoperative pain. However, it also carries an FDA warning against use in cats with
kidney dysfunction.⁴ In other 
countries, oral meloxicam is
labeled for longer use in cats. 
Dr. Scherk cited 3 Australian
 studies in which long-term
meloxicam administration
 did not adversely affect renal 
function or exacerbate renal
 disease in cats.^5-7 She pointed
 out that the US label dose 
for subcutaneous meloxicam 
injection (0.3 mg/kg) is much higher than the oral doses used in these studies (0.01-0.03 mg/kg).

Robenacoxib is labeled in the United States for 3-day use for control of postoperative pain in cats.⁸ One study’s results showed no worsening of kidney disease in cats treated with robenacoxib for 1 month, Dr. Scherk said.⁹

She suggested that veterinarians considering off-label use of NSAIDs in cats refer to consensus guidelines for NSAID use published in 2010 by the AAFP and the International Society of Feline Medicine. The guidelines, as well as brochures for cat owners, are available on the AAFP website.¹⁰ Dr. Scherk discussed some precautions for NSAID use in cats (see the guidelines for complete recommendations):

• Choose patients that are well hydrated and do not have congestive heart failure or moderate to severe kidney disease.

• Dose on the basis of lean body weight, not the actual weight, of overweight cats.

• Use the lowest effective dose.


• Combine use with other modalities, such as environmental modification, in addition to the NSAID.


• Maintain ongoing communication with the cat owner, and discontinue the drug immediately if adverse events occur.


• Do not use NSAIDs concurrently with corticosteroids or other drugs that pose an interaction risk.


• Check bloodwork at least every 6 months, more often in high-risk patients.

Opioids

Opioids are the cornerstone of managing moderate to severe pain, Dr. Scherk said. They are safe to use in all ages, can be given concurrently with NSAIDs, and are useful for treating perioperative pain. They are not particularly effective as sole agents for OA pain. Opioids also can be used to treat breakthrough pain in cats taking NSAIDs and to manage short-term procedural pain, she said. Various potencies and durations are available.

Other Agents

Xylazine, dexmedetamidine, and other α₂-adrenoceptor agonists may be helpful for supplemental analgesia in cats but should not be used in those with cardiovascular disease or other hemodynamic diseases, Dr. Scherk said. Ketamine and amantadine are both NMDA receptor antagonists. Ketamine is generally administered for a short time in the hospital, and amantadine can be given orally at home. Gabapentin may be helpful for neuropathic pain.

New Possibilities

Dr. Scherk discussed a few novel agents that are in development or available for other species. A monoclonal antibody against nerve growth factor, a substance involved in inflammatory pathways, is undergoing clinical trials in cats. Grapiprant is a prostaglandin receptor antagonist that has been approved for use in dogs but not in cats. Cannabinoids have not been investigated in cats, and Dr. Scherk warned the audience about the toxicity of products containing tetrahydrocannabinol.

Home Care

Environmental modification is an important component of pain management, Dr. Scherk said. The goal is to allow cats to return to normal activities. “[It’s] super important that cats get to do catlike things and be happy doing them,” she said. Ramps and steps, padded bedding, and raised water and food bowls can make cats more comfortable, and litter box sides should be low enough for cats with arthritis to enter comfortably.

Additional suggestions include dietary joint supplements, which may be helpful for cats with OA; weight reduction for overweight cats; and trimming nails to keep them from snagging on carpet and to maintain correct joint alignment, Dr. Scherk said. Physical rehabilitation (therapeutic exercise) may also be of benefit.

CONCLUSIONS

“The experience of pain is different for every individual,” Dr. Scherk said. The analgesic plan should be tailored to each cat. She stressed following up with owners regularly to assess response to treatment and adjusting each cat’s management plan as needed.

References

1. Mathews K, Kronen PW, Lascelles D, et al. Guidelines for recognition, assessment and treatment of pain. J Small Anim Pract. 2014;55(6):E10-E68. doi: 10.1111/jsap.12200.

2. Feline musculoskeletal pain index. NC State College of Veterinary Medicine website. https://cvm.ncsu.edu/research/labs/clinical-sciences/comparative-pain-research/labs-comparative-pain-research-clinical-metrology-instruments-subjective-nighttime-restlessness-evaluation-snore/?rel=0" ?rel=0" . Accessed November 9, 2018.

3. Epstein M, Rodan I, Griffenhagen G, et al. 2015 AAHA/AAFP pain management guidelines for dogs and cats. American Animal Hospital Association website. aaha.org/public_documents/professional/guidelines/2015_aaha_aafp_pain_management_guidelines_for_dogs_and_cats.pdf. Accessed November 9, 2018.

4. Metacam [package insert for cats]. St. Joseph, MO: Boehringer Ingelheim Vetmedica GmbH; 2014.

5. Gunew MN, Menrath VH, Marshall RD. Long-term safety, efficacy and palatability of oral meloxicam at 0.01-0.03 mg/kg for treatment of osteoarthritic pain in cats. J Feline Med Surg. 2008;10(3):235-241. doi: 10.1016/j.jfms.2007.10.007.

6. Gowan RA, Lingard AE, Johnston L, Stansen W, Brown SA, Malik R. 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. doi: 10.1016/j.jfms.2011.06.008.

7. 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. doi: 10.1177/1098612X12454418.

8. Onsior [package insert]. Greenfield, IN: Elanco US Inc; 2015.

9. King JN, King S, Budsberg SC, et al. Clinical safety of robenacoxib in feline osteoarthritis: results of a randomized, blinded, placebo-controlled clinical trial. J Feline Med Surg. 2016;18(8):632-642. doi: 10.1177/1098612X15590870.

10. Gunn-Moore D. 2010 AAFP/ISFM long term use of NSAIDS in cats. American Association of Feline Practitioners website. catvets.com/guidelines/practice-guidelines/nsaids-in-cats. Accessed November 9, 2018.

Dr. Walden received her DVM from North Carolina State University and completed an internship in small animal medicine and surgery at Auburn University. She is a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. Dr. Walden writes and edits materials dealing with most areas of human and veterinary medicine. She has also been a practicing primary care veterinarian for many years.