Assessing Chronic Pain In Dogs
Finding precise, reliable, and accurate measures of chronic pain in animals is a difficult effort. However, much research has gone into developing measurement methods to evaluate chronic pain in dogs (and, more recently, cats); this article reviews the pain scales currently available.
One thing clinicians and investigators can agree upon is that finding valid, precise, reliable, and accurate measures of chronic pain in animals is a very tall order indeed. However, the effort is important—if we are to effectively manage patients with chronic pain, we have to be able to assess it, which also allows us to determine whether our interventions are therapeutic.
QUALITY OF LIFE
Chronic pain significantly impacts quality of life in animals, as it does in humans. In addition to the discomfort itself, there is diminished mobility and ability to perform normal activities of daily living. In humans, chronic pain is associated with cognitive deficits (learning, memory, etc) and increasingly understood to coexist with clinical depression.1,2 Other, nonpainful conditions can influence chronic pain assessment, including neurologic and metabolic disease.
PAIN ASSESSMENT METHODS
There are 5 prospective methods to assess and score chronic pain:
- Veterinary examination
- Physiologic biomarkers
- Objective measurements of gait (eg, force plate) and/or activity and movement (eg, accelerometer)
- Owner assessment of activities of daily living (ADL)
- Multifactorial clinical measurement instruments.
Unfortunately, veterinarians have found chronic pain scoring based on physical examination disappointing. Reasons include:
- Variability among veterinary observers and even among examinations by the same veterinarian
- Variable expression of pain among patients
- Change of patient behavior in examination room versus at home
- Many different causes of chronic pain.
Currently there are no biomarkers (biochemical or physiologic parameters) that reliably correlate to chronic pain, although this is an area under active investigation. Physiologic biomarkers, such as blood pressure, heart rate, and cortisol levels, have very low specificity because circumstances other than pain (eg, fear, anxiety, stress) also affect these markers.
OBJECTIVE MEASUREMENTS OF GAIT
Objective measurements, such as force plate analysis or activity monitors, when properly utilized, are valid in the research setting but, at this time, have not translated into clinical practice. As technology advances, these may be promising clinical modalities in the near future.
OWNER ASSESSMENT OF ADL
Owner assessment of ADL is currently the most scientifically and clinically useful chronic pain scoring tool.
The most common chronic pain condition encountered in dogs and cats is osteoarthritis (OA); other conditions that can cause chronic pain include intervertebral disk disease, cancer, and nonmalignant neuropathies/myopathies.
The clinical observations owners generally make are related to behavior changes in their pets. Clients most often notice the growing absence of behaviors once considered routine (diminished abilities or disability); less often they notice onset of new behaviors (eg, lameness, vocalization).
Several challenges exist when relying on owner observations to evaluate chronic pain in pets:
- Some behaviors associated with chronic pain, such as diminished abilities and mobility challenges, may also be attributed to nonpainful conditions, such as neurologic or metabolic disease.
- If a pet’s pain is associated with OA, asking untrained owners to simply assign a visual analogue scale number of 0 to 10 to quantify pain is a poor tool because of inferior observational validity (ie, owners may not recognize certain behavior as signs of pain).3
- Differences in manifestations of chronic pain among species—specifically OA-related behaviors—make it difficult to apply specific pain scoring systems to both dogs and cats.
CLINICAL MEASUREMENT INSTRUMENTS
Due to the limitations and challenges noted above, observation-based owner questionnaires and multifactorial clinical measurement instruments (CMIs) have been developed and validated in animals and humans, with the latter often inspiring the former.
Before questionnaires and CMIs are considered ready for clinical use, an extensive development process evaluates several levels and layers of validity. To learn more about this validation process, visit the North Carolina State University Comparative Pain Research Laboratory’s webpage on Clinical Metrology Instruments at cvm.ncsu.edu/docs/cprl/cmi.html.
Several CMIs have been validated in dogs and others are under development in cats.
Helsinki Chronic Pain Index
The Helsinki Chronic Pain Index (HCPI) for dogs with OA was first described in 20034 and then validated in 2009.5
For the HCPI, 11 items are scored 0 to 4, divided between a:
- Simple Descriptive Scale for demeanor, behavior, and locomotion
- Visual Analog Scale for pain and locomotion.
This system has also been used to assess response to nutritional therapy for OA.6,7 In one study, HCPI correlated well with improvements of objective gait assessments in the study group; however, improvement in HCPI was also seen in the placebo group while objective measurements worsened.8 The paradox of these results speaks to the inherent challenges and limitations of not only CMIs but also objective measurements.
Canine Brief Pain Index
The Canine Brief Pain Index (CBPI) was adapted from a human Brief Pain Index and validated for canine OA in 20079 and osteosarcoma in 2009.10
The CBPI asks owners to assign a score to 11 domains.
- Four domains involve pain severity: the owner assigns a numerical rating score of 0 (no pain) to 10 (severe pain) to the pet’s Worst, Least, Current, and Average pain over the previous 7 days.
- Six domains involve pain interference with function: the owner assigns a 0 (no interference) to 10 (complete interference) to General Activity, Enjoyment of Life, Ability to Rise to Standing, Ability to Walk, Ability to Run, and Ability to Climb Stairs.
- The final domain involves quality of life: the owner assesses the dog’s general quality of life from 0 (poor) to 5 (excellent).
- The patient score is the sum of these domains.
The CBPI has been successfully used to assess response to therapy for OA11,12 and, more recently, it has been shown to correlate with objective measurements of canine OA.13
Cincinnati Orthopedic Disability Index
Developed in 2003,14 the Cincinnati Orthopedic Disability Index (CODI) uses client-specific outcome measures (CSOMs), making it different from other tools.
Instead of relying on the same standard questions for each patient, the CODI asks owners what difficulties they believe their dogs are exhibiting.
- For each activity, the owner notes if it is a Little Bit of a Problem, Quite a Bit of a Problem, a Severe Problem, or Impossible for the dog to do.
- Answers are assigned a score of 1 to 4, respectively; then transformed into a 0 to 100 score, with 100 denoting a perfectly normal dog. The score decreases with increasing degrees of disability.
The CODI has been used to assess an adjunctive pain modifying drug15 and, recently in a trial investigating a canine OA food, it correlated well with objective measurements (gait analyses) and outperformed CBPI and the Health-Related Quality of Life (HRQL) CMI in evaluating response to therapy.16
CSOMs may have cross-over application to assessing OA in cats.17
Health-Related Quality of Life (Glasgow University Health-Related Dog Behaviour Questionnaire)
The Health-Related Quality of Life (HRQL) was developed specifically for veterinary patients versus being derived from an existing CMI for humans.
- The HRQL was first published to evaluate the impact of pain on quality of life in dogs with OA (2004, 2006),18,19 and osteosarcoma (2005).20
- The OA HRQL asks owners to score 109 items (therefore, it is time-consuming) in 12 domains on a 1 to 7 scale, while the Osteosarcoma HRQL is simpler, with only 12 items to score, including:
- Ability to play
- Gastrointestinal function
- Interaction with family members
- Presence of pain
The original OA HRQL was recently (2013) refined and reduced to include only 46 items that fall under 4 domains:21
- Anxiety: Feeling of worry, nervousness, or unease
- Pain: An unpleasant sensory and emotional experience associated with actual or potential tissue damage
- Stress: A state of mental or emotional strain or tension resulting from adverse or very demanding circumstances
- Vitality: Physical or mental vigor; capacity for survival or for the continuation of a meaningful or purposeful existence.
Liverpool Osteoarthritis in Dogs
The Liverpool Osteoarthritis in Dogs (LOAD) CMI was first validated to evaluate canine elbow arthritis (2009)22; however, it also compares favorably with HRQL and CBPI and correlates (albeit weakly) with objective measurements (gait analyses).23 LOAD asks owners to assess their dogs’ mobility in 13 areas (5 General domains and 8 At Exercise domains) on a 0 to 4 Simple Descriptive Scale.
In the near future, practitioners can expect to see one or more of these chronic pain scoring tools adapted for use in the clinical setting. With widespread use, our ability to follow patients with chronic pain, and adjust their management accordingly, can be expected to improve significantly.
Canine CMIs: Where to Find Them
- Helsinki Chronic Pain Index: The second English translation of the HCPI can be found at http://www.vetmed.helsinki.fi/english/ animalpain/hcpi/HCPI_E2.pdf.
- Canine Brief Pain Index: A PDF of the CBPI is available at https://centri.unipg.it/cesda/doc/files/scale_del_dolore/ Canine_Brief_Pain_Inventory.pdf.
- Cincinnati Orthopedic Disability Index: The CODI is available on the IVAPM’s website at ivapm.org (for members), and is also available at todaysveterinarypractice.com.
- Health-Related Quality of Life: The latest version of this CMI is described in Development, Validation and Reliability of a Web-Based Questionnaire to Measure Health-Related Quality of Life in Dogs, available at http://onlinelibrary.wiley.com/ doi/10.1111/jsap.12059/abstract.
- Liverpool Osteoarthritis in Dogs: Read Evaluation of Construct and Criterion Validity for the ‘Liverpool Osteoarthritis in Dogs’ (LOAD) Clinical Metrology Instrument and Comparison to Two Other Instruments at http://www.plosone.org/article/info:doi/ 10.1371/journal.pone.0058125.
Scoring Feline Osteoarthritis
Feline OA appears to have a different etiopathophysiology than OA in dogs, and fundamental peculiarities of feline behavior appear to create a strong placebo effect in pain studies.
Development of a valid CMI for this species is an area of active investigation:
- An initial CMI is modeled after the CBPI and evaluates 16 different domains, including grooming, eating, jumping, and play behaviors.24
- A Feline Musculoskeletal Pain Index has been developed (cvm.ncsu.edu/docs/cprl/fmpi.html). It measures the impact of OA on the domains of: pain (adverse sensory and emotional experience), mobility (quality of moving freely), activity (ability to perform specific activities), and affective effects (mood, as perceived by those caring for the cat).25
ADL = activities of daily living; CBPI = Canine Brief Pain Index; CMI = clinical measurement instrument; CODI = Cincinnati Orthopedic Disability Index; CSOM = client-specific outcome measures; HCPI = Helsinki Chronic Pain Index; HRQL = Health-Related Quality of Life; IVAPM = International Veterinary Academy of Pain Management; LOAD = Liverpool Osteoarthritis in Dogs; OA = osteoarthritis
- Kreitler S, Niv D. Cognitive impairment in chronic pain. Pain Clinical Updates 2007; XV(4).
- Giordano J, Wurzman R. The possibility and plausibility of putative neurophsychiatric spectrum disorders. Depression: Mind, Body 2008; 4(1):2-5.
- Hielm-Björkman AK, Kapatkin AS, Rita HJ. Reliability and validity of a visual analogue scale used by owners to measure chronic pain attributable to osteoarthritis in their dogs. Am J Vet Res 2011; 72(5):601-607.
- Hielm-Björkman AK, Kuusela E, Liman A, et al. Evaluation of methods for assessment of pain associated with chronic osteoarthritis in dogs. JAVMA 2003; 222(11):1552-1558.
- Hielm-Björkman AK, Rita H, Tulamo RM. Psychometric testing of the Helsinki chronic pain index by completion of a questionnaire in Finnish by owners of dogs with chronic signs of pain caused by osteoarthritis. Am J Vet Res 2009; 70(6):727-734.
- Hielm-Björkman A, Tulamo RM, Salonen H, Raekallio M. Evaluating complementary therapies for canine osteoarthritis—Part I: Green-lipped mussel (Perna canaliculus). Evid Based Complement Alternat Med 2009; 6(3):365-373.
- Hielm-Björkman A, Tulamo RM, Salonen H, Raekallio M. Evaluating complementary therapies for canine osteoarthritis—Part II: A homeopathic combination preparation (Zeel). Evid Based Complement Alternat Med 2009; 6(4):465-471.
- Hielm-Björkman A, Roine J, Elo K, et al. An uncommissioned randomized, placebo-controlled double-blind study to test the effect of deep sea fish oil as a pain reliever for dogs suffering from canine OA. BMC Vet Res 2012; 8:157.
- Cimino-Brown D, Boston RC, Coyne JC, Farrar JT. Development and psychometric testing of an instrument designed to measure chronic pain in dogs with osteoarthritis. Am J Vet Res 2007; 68:631-637.
- Brown DC, Boston R, Coyne JC, Farrar JT. A novel approach to the use of animals in studies of pain: Validation of the canine brief pain inventory in canine bone cancer. Pain Med 2009; 10(1):133-142.
- Brown DC, Boston RC, Coyne JC, Farrar JT. Ability of the canine brief pain inventory to detect response to treatment in dogs with osteoarthritis. JAVMA 2008; 233(8):1278-1283.
- Sullivan MO, Gordon-Evans WJ, Knap KE, Evans RB. Randomized, controlled clinical trial evaluating the efficacy of pulsed signal therapy in dogs with osteoarthritis. Vet Surg 2013; 42(3):250-254.
- Brown DC, Boston RC, Farrar JT. Comparison of force plate gait analysis and owner assessment of pain using the Canine Brief Pain Inventory in dogs with osteoarthritis. J Vet Intern Med 2013; 27(1):22-30.
- 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(4):376-386.
- Lascelles BD, Gaynor JS, Smith ES, et al. Amantadine in a multimodal analgesic regimen for alleviation of refractory osteoarthritis pain in dogs. J Vet Intern Med 2008; 22(1):53-59.
- Rialland P, Bichot S, Moreau M, et al. Clinical validity of outcome pain measures in naturally occurring canine osteoarthritis. BMC Vet Res 2012; 8:162.
- Lascelles BD, Hansen BD, Roe S, et al. Evaluation of client-specific outcome measures and activity monitoring to measure pain relief in cats with osteoarthritis. J Vet Intern Med 2007; 21(3):410-416.
- Wiseman-Orr ML, Nolan AM, Reid J, Scott EM. Development of a questionnaire to measure the effects of chronic pain on health-related quality of life in dogs. Am J Vet Res 2004; 65(8):1077-1084.
- Wiseman-Orr ML, Scott EM, Reid J, Nolan AM. Validation of a structured questionnaire as an instrument to measure chronic pain in dogs on the basis of effects on health-related quality of life. Am J Vet Res 2006; 67(11):1826-1836.
- Yazbek KV, Fantoni DT. Validity of a health-related quality-of-life scale for dogs with signs of pain secondary to cancer. JAVMA 2005; 226(8):1354-1358.
- Reid J, Wiseman-Orr ML, Scott EM, Nolan AM. Development, validation and reliability of a web-based questionnaire to measure health-related quality of life in dogs. J Small Anim Pract 2013; 54(5):227-233.
- Hercock CA, Pinchbeck G, Giejda A, et al. Validation of a client-based clinical metrology instrument for the evaluation of canine elbow osteoarthritis. J Small Anim Pract 2009; 50(6):266-271.
- Walton MB, Cowderoy E, Lascelles D, Innes JF. Evaluation of construct and criterion validity for the ‘Liverpool Osteoarthritis in Dogs’ (LOAD) clinical metrology instrument and comparison to two other instruments. PLoS One 2013; 8(3):E58125. DOI: 10.1371/journal.pone.0058125.
- Zamprogno H, Hansen BD, Bondell HD, et al. Item generation and design testing of a questionnaire to assess degenerative joint disease-associated pain in cats. Am J Vet Res 2010; 71(12):1417-1424.
- Benito J, Hansen B, DePuy V, et al. Feline Musculoskeletal Pain Index (FMPI): Responsiveness and criterion validity testing. J Vet Intern Med 2013; doi: 10.1111/jvim.12077.