A seemingly ‘simple’ disease such as arthritis can be associated with multiple sources and types of pain – listen to a brief overview here
Pitfalls in analgesic trials
Quality of life in chronic pain
Pain is commonly considered a marker of negative welfare, and the importance of preventing pain in animals is reflected within a number of laws in the UK e.g. the Animal Welfare Act 2006 provides a duty of care on animal owners to prevent or treat pain, suffering, injury, and disease.
When we consider welfare we try to consider all aspects of the animal – not just its physical sensations, but its emotional responses and how it interacts with the environment in which it lives.
So how does pain impact welfare? And are there any strategies we can consider to modify these impacts?
We can consider three different levels of pain processing within the body. The firest level is the spinal cord, which co-ordinates reflex (unconscious) movements to avoid acutely painful stimuli.
Acute, nociceptive pain is a physical process without much emotional or cognitive processing. In fact, when we accidentally touch something dangerously hot, the nerve impulses cause our muscles to contract and pull our hand away from the source of pain before we are even consciously aware of the sensation – the “ouch!” comes later.
Some spinal cord nerve cells project toward the brain, and if pain continues these transmit information in the form of electrical signals.
At lower levels of the brain these projected pain signals activate areas associated with behavioural motivation, such as the anterior cingulate cortex and insula. These centres mediate the ‘affective’ component of pain, which can be considered as how the pain makes us feel emotionally. This activation causes an increased vigilance and alertness, recognised as the ‘fight, flight, or freeze’ response, and is associated with increased stress hormone release such as noradrenaline and cortisol. In cases of ongoing pain and continued activation of these brain centres, animals may find it difficult to regulate their emotions and exhibit behavioural issues, including increased noise sensitivity and aggression. In humans with chronic pain there is a clear association between physical pain and emotional suffering exhibited as anxiety and depression. It is the emotional unpleasantness of pain which motivates the animal experiencing it to fight, run away, or freeze. Although these behaviours might be helpful to ameliorate an acute threat of pain, in longer term pain these behaviours don’t mediate an escape from pain, and so the motivations remain.
Finally the pain signalling reaches the cerebral cortex, which mediates the conscious perception of pain, in terms of where in the body it is and how intense it is. In people with ongoing pain there are effects on learning, memory, and concentration, so It may be that ‘trainability’ and other executive functions of the dog’s mind are affected by pain.
Although it is most straightforward for us to recognise the conscious perception of pain as ‘suffering’, seeing animals directing their attention to painful areas, or limping, it is important that we recognise that the unconscious emotional aspects and resulting sympathetic nervous system activation will also impact the animal, and could also be considered suffering.
Exaggerated fight and flight responses can impact pet and owner relationships – if your dog is lunging at other dogs it can be difficult to have sympathy with them, even when we are aware that they may have a source of pain. It’s not much fun for them either, and over time the increased levels of stress hormones are likely to accelerate their aging processes.
Whilst pain can negatively impact emotions and cognitive function, evidence from people suggests that positive emotional states might be able to reduce pain, so while we cannot replace the need for effective vet-led pain management, it is probably worth considering ways in which we might be able to influence emotions in animals.
Training pain free dogs in a foraging task for food led to improvements in cognitive bias (a measure of optimism in dogs) compared to a group trained in heelwork1. Although data are not available for dogs affected by painful conditions, simple tasks such as these promote gentle movement and may have an additional emotional benefit, so seem well worth doing. Physiotherapy was reported to have a positive effect on the psychological domain within a canine quality of life scale2.
Some evidence exists of the stress relieving properties of essential oils such as lavender3 and ginger4 for dogs in kennel environments – it is possible that these effects could also occur in the home environment. These products should never be applied directly to animals but can be applied to cloths or tissues placed (out of pet’s reach) around the home. It is important to note that there are reports of toxicity associated with use of essential oils, particularly in cats5, so careful use is vital.
The mind-body connection is not purely a human phenomenon, and we are beginning to learn ways in which we can improve welfare by addressing all aspects of an animal’s experience.
1.Duranton, C. & Horowitz, A. Let me sniff! Nosework induces positive judgment bias in pet dogs. Appl Anim Behav Sci 211, 61–66 (2019).
2.Piotti, P., Albertini, M., Lavesi, E., Ferri, A. & Pirrone, F. Physiotherapy Improves Dogs’ Quality of Life Measured with the Milan Pet Quality of Life Scale: Is Pain Involved? Vet Sci 9, 335 (2022).
3.Amaya, V., Paterson, M. B. A. & Phillips, C. J. C. Effects of Olfactory and Auditory Enrichment on the Behaviour of Shelter Dogs. Animals 10, 581 (2020).
4.Binks, J., Taylor, S., Wills, A. & Montrose, V. T. The behavioural effects of olfactory stimulation on dogs at a rescue shelter. Appl Anim Behav Sci 202, 69–76 (2018).
5. Online https://www.cats.org.uk/cats-blog/cats-and-essential-oils [accessed 19th November 2022]
Treatment of femoral neuropathic pain
In some cases of neuropathic pain, steroid treatments can be helpful. Depending on the source of the pain it may be possible to administer long acting injections close to the painful nerve.
Scents and sensibility
A recently published paper investigated links between depression and olfactory function in people. The researchers found that their data supported the hypothesis that an increase in olfactory function was associated with a decrease in depression severity. Persistent pain can impact on many different domains of life, including mobility, social and feeding behaviour, sleep, and mood. Diagnosing mood problems in pets may be challenging, and there are few licensed medications available for treatment, but encouraging dogs to use their sense of smell might contribute to improved mood. Depending on the degree of mobility of the pet, simply using part of their daily food ration to scatter around a non-slip area, with a few simple areas to investigate such empty boxes, can provide mental stimulation. More mobile dogs can be taught a degree of scent training – the target scent such as cloves or gun oil is associated with a food reward, and ultimately the dog can be taught to search for the target scent. This activity is excellent as it provides low- to moderate-intensity physical exercise and engages the olfactory portion of the dog’s brain. Finding toys by scent is another option for toy-centric canines.
How do we interpret studies on pain in animals?
This one is a bit technical, and intended for those who are looking at and interpreting primary source papers – just some of the things I try to think about as I read them – do you agree?
The expansion of studies evaluating treatment of pain in animals is a significant achievement for veterinary medicine and animal welfare, but science isn’t always clear-cut. Sometimes results are unexpected and differ from previous findings. Abstracts are necessarily concise, and may not reflect all of the considerations pertaining to patients.
How, then, should we assess scientific investigations into putative analgesics to treat our clinical cases?
Our first considerations are related to be the study design. Is this a retrospective case series without a control group? in which case any treatment effect may be confounded by care-giver placebo effects and regression to the mean (spontaneous improvements in disease state). Is this a placebo-controlled cross over study, in which owner and investigator are unaware of treatment allocation (‘double-masked’)? If the order of treatment and placebo administration blocks is randomised, then this study design enables each animal to act as its own control, and can be a powerful study design to detect treatment effects. A placebo-controlled double masked grouped study can provide evidence of treatment effect if the control group is appropriately matched to the treatment group.
In pain medicine we have very few magic bullets – it is unlikely that a single intervention will provide total relief, and so investigators need to make a decision whether to test the new intervention is isolation (although the treatment effect will need to be very large, or a large sample size may be necessary to demonstrate a more modest effect), or to evaluate the treatment in addition to current care (which most patients will already have established).
The sample size of the study needs to be large enough so that clinically relevant differences would be identified with statistical testing – this requires investigators to make assumptions about the size of treatment effect they expect, and also regarding the natural variance within the population – if these assumptions are incorrect then the results may need careful evaluation.
Persistent pain impacts many areas, or domains, of a patient’s life. Although these may be interlinked, it is likely that treatments will benefit some areas more than others. Therefore, the particular outcome measures which are being investigated by a study may be more or less relevant to our patients. Examples of outcome measures might include objective measures of limb use in appendicular osteoarthritis, subjective evaluations of function using client specific outcome measures, total activity or activity patterns over the day using collar mounted accelerometers, skin or muscle sensitivity using sensory testing measures, clinical metrology instrument (CMI) scores to evaluate pain and quality of life, and dose of ‘rescue’ analgesics administered. Different outcome measures should ideally be validated – for example many CMIs are validated only in certain painful conditions. Side effects of drugs used in interventions should also be considered – for example increased locomotor activity may be associated with pain free movement, but can be associated with the use of opioid drugs.
It is possible that some interventions may improve pain relief and quality of life without necessarily increasing activity, or changing distribution of weight.
We should also carefully consider the attributes of the patients in the study and how closely these relate to our patients. Although osteoarthritis patients all present with a degree of synovitis and cartilage damage, the severity of these is variable and the secondary changes (myofascial pain, neuroplasticity, muscle atrophy) may further increase the variability between patients. Different patients with differing degrees of secondary changes may respond differently to analgesic interventions – therefore defining these characteristics in study populations is important. Less common pain conditions are likely to be even more variable, and difficult to perform clinical studies.
In the future pharmacogenomics may provide information on how individual patients process pain signals and respond to analgesics, and could be an exciting area for future developments.
Thoughts about supplements
Joint supplements are so widely available and heavily advertised that one would be forgiven for thinking their benefits in managing osteoarthritis are undoubted. But, the evidence available is mixed. The most consistent evidence demonstrates improvements in mobility in dogs with ostearthritis treated with marine sourced omega-3 fatty acids. In some studies, the addition of omega-3 fatty acids to treatment with non-steroidal drugs were associated with larger improvements than in dogs treated with non-steroidal drugs alone. However, there is still a lack of placebo controlled data therefore it can be challenging to isolate benefits ascribed to supplements. Practical advice on using arthritis supplements in animals includes
- Seeking veterinary advice early – licensed veterinary treatments can be highly effective and may represent a better cost/benefit than trying supplements without vet involvement
- Using supplements from established and trusted sources – many supplements may contain less active or lower quality forms of ingredients so try to use those that have an established presence and ideally a guaranteed certificate of analysis
- Supplements (and drugs) can’t replace good lifestyle changes such as providing flooring with traction, maintaining a healthy body weight, and preventing injuries through adequate warm up and cool down activity.
One product which contains an adequate level of omega-3 fatty acids and is derived from green lipped mussels is available from https://antinol.co.uk/. For a 5% discount enter code VPUKPPR at the checkout page.
Supporting physical rehabilitation with behavioural modification
When managing painful conditions it is important to remain aware of the effects of pain on behaviour and conscious experience. By using pain-relieving medications, physical therapies, and cognitive activities we can reduce the impact of pain on quality of life. We also need to be aware that behaviours can negatively impact chronic pain conditions – for example uncontrolled racing/chasing can increase the risk of injuries (particularly if it involves explosive activity without warming up), or exacerbate pre-existing injuries.
Keeping more than one excited dog on a lead can be challenging!
By using some training techniques we can try to alter the excitement levels of dogs so that they go from racing through a gateway to sniffing for treats on the ground. We can get through the pinch point (gateway) and divert attention away from racing against each other towards calmer movement. We can then set off on our walk in a more relaxed frame of mind. Scattering some more treats as we go focusses attention on us, rather than the environment, and everyone gets a change to warm up before strenuous exercise.
Think about replacing chasing type activities (ball or frisbee throwing) with seeking/searching activities – these provide a great workout but greater focus and precision, which might reduce the risk of injury. Searching for food, toys, or more structured target scent training work provides mental and physical stimulation without subjecting the body to the forces associated with jumping, twisting, and sprinting and can be incredibly rewarding for dogs.
Why does it hurt?
Definitions of pain universally agree that it is an unpleasant experience, so why have we not evolved to live without it?
The answer is that pain is essential for animals to navigate safely within their environments, and evidence of pain sensation has been reported in studies of octopus and fish, birds, reptiles, and mammals. Detection of stimuli (heat, cold, pressure, or chemical) that have the potential to cause tissue damage enables the animal to avoid this immediate danger. Because tissues such as skin, muscle, and bone contain pain-sensing nerve endings, any damage that is caused to the animal generates pain which persists for the period of tissue healing. This has the benefit of reducing the use of damaged tissues and encouraging the animal to rest away from predators. One of the major functions of pain is the formation of memories, which increase the likelihood that animals will avoid the danger in the future. The unpleasantness of pain can be considered a ‘positive punishment’ in terms of training, which is why it creates effective learning but is also associated with increases in sympathetic activation, stress, and anxiety.
As we have seen, pain does confer an evolutionary advantage to animals. Unfortunately, it can be considered a double-edged sword. In some cases, even after the resolution of tissue damage, pain can persist (e.g. after surgery or amputation) and become a disease in itself. In other cases signals which are associated with tissue damage occur on an ongoing basis (e.g. inflammation in osteoarthritis, muscle pain). Finally, we can see situations where the nervous system begins to generate pain independently of any tissue damage.
Because pain is unpleasant and generates feelings of stress and anxiety, ongoing pain conditions represent a significant welfare problem but fortunately, thanks to the hard work of many researchers, the knowledge of vets and allied professionals in managing pain has vastly increased over the past decade. In common with human pain conditions, we recognise that a multi-disciplinary team is often necessary for optimal management of pain in animals and that obtaining an accurate diagnosis is often the first step in a long road to recovery. But as we know, a journey of a thousand miles begins with one step.
If you are worried that your pet may be experiencing a painful condition, do speak to your vet. If they think it necessary there are now a number of highly trained vets across the country who can offer advice or accept referral cases for pain management.
Getting to the point – acupuncture in dogs and cats
In the previous blog post we discussed the contribution that muscle pain can make to the overall pain experience associated with osteoarthritis.
Acupuncture has been suggested to have three main benefits in the treatment of chronic pain. Firstly, by targeting the muscle trigger points, which can be identified by careful clinical examination by a veterinary surgeon, acupuncture can help to relieve the tension and associated pain in these points and help restore normal muscle function.
Secondly the introduction of the fine needles into the muscle triggers the body to produce natural pain killing endorphins, which decrease pain and induce relaxation.
Finally, a medical electroacupuncture device can be used to apply a gentle high frequency pulse between pairs of acupuncture needles, which can have a powerful effect on decreasing sensitivity in nerves in the spine and reducing nerve pain.
Acupuncture is classed as an act of veterinary surgery in the UK and can only be performed by a qualified veterinary surgeon. Although it is not a skill that all vets are taught, there are some excellent courses available.
James attended the four day Western Veterinary Acupuncture Course in 2010 and has been performing acupuncture and electroacupuncture on animals since.