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Management of chronic pain in small animals

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01 May 2015, at 12:00am

GWEN COVEY-CRUMP examines the myriad of considerations and treatment options available to veterinary surgeons as pets live longer, beginning in the home with client education

AS pets live longer, with advances in veterinary medicine chronic pain is becoming an increasingly common presentation. However, our ability to recognise and treat it is still in its infancy. In contrast to acute pain, the key to recognition of chronic pain is client education. Owners are best placed to observe their pets in the home environment and are most likely to engage with the process when you can document progress with the appropriate use of pain scales and questionnaires.

In contrast to acute pain, chronic pain may continue long after the inciting cause has resolved. Pain of high intensity and/or prolonged duration may result in neuroplastic changes within the central nervous system (central sensitisation). Pain is modulated at multiple levels (Figure 1) and these provide potential targets for analgesics and adjunctive therapy.

Triggers may include osteoarthritis, nerve impingement, cancer pain, gastrointestinal, aural and ophthalmic pain among others (AAHA/AAFP Pain Management Guidelines). Frequently, the pain experienced may not correlate with changes seen radiographically (Lascelles et al, 2012) and be remote from the inciting cause.

Changes in gait, posture and activity results in muscle weakness, altered load bearing of joint surfaces and pain in muscles and fascia.

The extent of “suffering” in chronic pain in humans is related more to the musculoskeletal response than simply with the original source of pain (Arendt-Nielsen and Graven-Nielsen, 2011).

Pain assessment

Pain assessment is considered to be more difficult in chronic pain as an animal learns to adapt its behaviours to its discomfort. Clients frequently refer to how stoic their pet seems to be but subtle behaviours have led them to believe the animal is suffering.

Observation of the animal in the non-stressful home environment, noting spontaneous behaviour as well as changes in willingness to play, interact and exercise, are more useful than measures used in acute pain. Tools such as the canine brief pain inventory have been validated in dogs (CiminoBrown et al, 2008 & 2009) and prove suitable for clients to use at home as a method of monitoring progress and response to therapy.

Cats provide more of a challenge as many of these markers are more difficult to assess. Response to a trial of a non-steroidal anti-inflammatory drug (NSAID) is a quick and easy method of subjectively demonstrating the presence of pain in cats but the use of client specific outcome measures (CSOMS) provides a more structured measure of progress (Lascelles and Robertson, 2010). CSOMS, also suitable for use in dogs, aim to identify typical normal behaviours that are impaired by pain. These are specified for a certain location and time of the day. Improvement or deterioration of these behaviours is then scored by the client over a given period of time.

For example:

  • Does the cat stretch to use his scratching post after coming in from his morning walkabout?
  • Does the dog greet its owners at the front door with a toy when they arrive home after work?
  • Does the dog join the family in the living room in the evening or stay in his bed in the kitchen?
  • How easy does the dog negotiate steps first thing in the morning?
  • Can the cat jump onto the kitchen worktop at feeding time?

A recent study evaluating a new feline musculoskeletal pain index (FMPI) demonstrated owners’ ability to detect pain in their cats with degenerative joint disease (Benito et al, 2013). However, the study was small and failed to differentiate between mild and severe pain. More work with a greater number of subjects is needed to validate this tool.

Physical examination

Lameness evaluation is important in identifying areas of pain but requires time and experience. Over-reliance on lameness examination alone may cause the clinician to miss problem areas especially in states of chronic pain. Signs of pain include tenderness, weakness, muscle tremor, limited range of motion and stiffness (IASP, 2009).

The manner in which a thorough physical examination is carried out is important in both maintaining/gaining trust from the patient and client but also identifying the real source of pain. Muscles should be palpated gently and limbs stretched very slowly and sometimes the clinician may need to introduce analgesic therapy prior to making a full assessment.

Treatment options

The pain management toolkit

General practitioners may dip into their pain management “toolkit” to form a tailored pain management plan which may include dietary modification and weight management; careful (but not over-zealous) exercise restriction; environmental adjustments; acupuncture; physiotherapy and hydrotherapy.

Pharmacological therapy includes both veterinary licensed drugs and centrally acting drugs licensed for use in humans. An outline of potentially useful drugs is provided here for reference (Table 1). Multi-modal therapy (to include complementary therapies below) may reduce sideeffects and enhance the response to treatment.

Dietary modification

Numerous studies have confirmed the risk obesity poses for pain and lameness in dogs and humans with osteoarthritis (Marshall et al, 2010). Maintenance of core muscle tone is key to managing pain in older dogs and this can be achieved with physiotherapy combined with dietary modification. So-called “senior” diets fed with restricted protein content should be used with care in a patient already struggling to maintain muscle mass and the feeding of restricted quantities of high-quality digestible protein is important.

Environmental adjustments

These may include positioning mats on laminate floors, improving ease of access to cars, beds, litter trays and favourite “perches” for cats. Providing multiple bedding substrates will help the owner to discover that which the pet favours.

Physiotherapy and hydrotherapy

Many practitioners will not have direct access to an underwater treadmill (UWT) or physiotherapist but increasing numbers of referral facilities are opening up around the country. Physiotherapy aims to restore function and movement and therefore assist with pain management whilst treating the patient as a whole system rather than a localised painful focus (Davies, 2014).

Treatment may range from use of manual therapy, ultrasound, laser, thermotherapy or cryotherapy to external co-aptation to encourage weight bearing in a functional manner (Figure 2). For hydrotherapy the UWT is preferred to swimming in a pool as, used appropriately, it promotes gentle weight bearing buoyant exercise with proprioceptive input to aid return to normal functional gait. Additional benefits include empowerment of the owners by learning to do exercises with their pet.

Acupuncture

Acupuncture (Figure 3) usually involves placement of fine needles into defined and other locations on the body. The effect of needle insertion is both peripheral and central. Electroacupuncture results in a direct segmental spinal cord inhibitory response without involvement of higher centres. Acupuncture influences central processing/modulation of pain with effects on expression of NMDA receptors and glial cells and neurotransmitters serotonin, noradreanaline and endorphines. Acupuncture may also increase opioid receptor binding in the limbic system. It is a useful tool to reduce the need for or side-effects to medication used for pain management.

It is important to manage client expectations from the outset, reminding them that treatment plans may need to be modified several times before the right outcome for the pet is achieved. Client engagement and commitment are key to success in the treatment of chronic pain.

Canine Brief Pain Inventory can be freely downloaded here: http://research.vet.upenn.edu/PennChart/AvailableTools/tabid/1969/Default.aspx.

References

Arendt-Nielsen, L., GravenNielsen, T. (2011) Translational musculoskeletal pain research. Best Prac & Res Clin Rheum 25: 209-226.

Benito, J. et al (2013) Reliability and discriminatory testing of a client based metrology instrument, feline musculoskeletal pain index (FMPI) for the evaluation of degenerative joint disease-associated pain in cats. Vet J 196 (3): 368-373.

Bortolami, E., Slingsby, L. and Love, E. J. (2012) Comparison of two formulations of buprenorphine in cats administered via the oral transmucosal route. J Fel Med Surg 14 (8): 534-539.

Cimino-Brown, D., Boston, R. C., Coyne, J. C. and Farar, J. T. (2008) Ability of the Canine Brief Pain Inventory to detect response to treatment in dogs with osteoarthritis. J Am Vet Med Assoc 233 (8): 1,278-1,283.

Cimino-Brown, D., Boston, R. C., Coyne, J. C. and Farar, J. T. (2009) A Novel Approach to the Use of Animals in Studies of Pain: Validation of the Canine Brief Pain Inventory in Canine Bone Cancer. Pain Medicine 10 (1): 133-142.

Davies, L. (2014) Canine Rehabilitation. In: Pain Management in Veterinary Practice. Eds Egger, C. M., Love, L., Doherty, T.P.: Wiley Blackwell. Hellyer, P., Rodan, I., Brunt, J. et al (2007) AAHA/ AAFP Pain Management Guidelines for Dogs and Cats. JAAHA 43: 235-248.

IASP – Exercise in Management of Musculoskeletal Pain. IASP Global Year Against Musculoskeletal Pain 2009-2010: web fact-sheet: www.iasp-pain.org.

Kogel, B., Terlinden, R. and Schneider, J. (2014) Characterisation of tramadol, morphine and tapentadol in an acute pain model in Beagle dogs. Vet Anaesth Analg 41 (3): 297-304.

KuKanich, B., Bidgood, T. and Knesl, O. (2012) Clinical pharmacology of non-steroidal antiinflammatory drugs in dogs. Vet Anaesth Analg 39: 69-90.

Lascelles, B. D. and Robertson, S. A. (2010) DJD-Associated Pain in Cats: what can we do to promote patient comfort? J Fel Med Surg 12: 200-212.

Lascelles, B. D., Dong, Y., Marcellin-Little, D. et al (2012) Relationship of orthopaedic examination, goniometric measurements, and radiographic signs of degenerative joint disease in cats. BMC Vet Res 8: 10.

Marshall, W. G., Hazewinkel, H. A. W., Mullen, D. et al (2010) The effect of weight loss on lameness in obese dogs with osteoarthritis. Vet Res Commun 34: 241-253.

Niyom, S., Mama, K. R., De Rezende, M. L. (2012) Comparison of the analgesic efficacy of oral ABT-116 administation with that of transmucosal buprenorphine administration in dogs. Am J Vet Res 73 (4): 476-481.

Sparkes, A. H., Heiene, R., Lascelles, B. D. et al (2010) ISFM and AAFP Consensus Guidelines Long-term use of NSAIDs in cats. J Fel Med Surg 12: 521-538