An article written by our Schools Education Manager, Rachel Jackson, for Animal Therapy Magazine
The symptom of pain is an essential part of life. Physiological pain is crucial for survival as it facilitates the identification of potentially harmful stimuli that can subsequently be avoided and allows for convalescence.
It is also one of the most common symptoms aiding human and animal medical/allied health care professionals in diagnosis and treatment. It is a well-known fact that pain is challenging to quantify and treat but understanding it can help us understand how patients feel and how to assist them effectively.
We often think pain is a simple cause and effect process. Reflex actions are part of this process, creating an automatic and fast response to a painful stimulus, thus minimising damage to the body. If humans or animals touch something hot, pain is generated on the skin’s surface and detected by nociceptors. This pain information is received in the spinal cord via sensory neurons, and then sent to the brain through ascending pathways where the pain information is received and processed in the somatosensory cortex. The efferent nerve fibres then carry the motor nerve signals to react to the stimulation by contracting the muscles and moving the limb away from the source of pain.
However, research shows that pain signalling, as well as the sensations the body perceives as pain, is more complex than this. Melzack and Wall (1965) (1) introduced the pain gate theory, which was an important step forward in the understanding of pain control. Their theory proposed that a gate control system modulated sensory input from the skin before it evoked pain perception and response. Thus, the spinal nerves act as gates to let pain information travel through to reach the brain. Open gates, too much pain is felt and for too long. Those with chronic pain conditions have gates that stay open when they should be shut. When the gates are closed, this prevents pain messages from getting through at all.
Since the introduction of this theory, revisions have been made in recognition of new understanding of physiology. Perhaps the most important contribution of the gate control theory is the way in which it changed thinking about pain perception. Melzack and Casey (1968) (2) differentiated three systems relating to the processing of nociceptive stimulation, all thought to contribute to the subjective experience of pain. These are sensory-discriminative, motivational-affective and cognitive-evaluative.
The gate control theory includes psychological factors as an integral aspect of the pain experience. Anxiety in people is associated with greater pain intensity (Lauriola et al. 2019)(3), prolonged elevation of pain levels, or anticipation of increased pain (Philips, 1988) (4). The links between pain and anxiety have been observed pre and post operatively and in chronic pain.
Understanding pain in humans is challenging, even with verbal communication. Human doctors can inquire about the location, intensity, duration and type of pain their patients experience. However, veterinarians face a unique challenge as their patients cannot communicate verbally. In the first instance, they rely on animal guardians recognising the subtle signs their companion displays if they are in pain. Such behavioural changes may be the first indication of a sub clinical condition. Recognition of these changes means they can be acted upon swiftly to limit the amount and time an animal is in pain, making it easier to get under control.
Pain in animals is often recognised by behavioural and physical changes. However, it is important to note that pain and responses to pain are individual, so what may be observed in one animal may be different in another. These changes may include:
VOCALISATIONS barking, whining, crying or a long, low sigh.
DAILY HABITS withdrawing from contact; sleeping in a different place; sleeping, drinking or eating more or less; not going up and down stairs.
SELF-MUTILATION licking, scratching, biting or nibbling parts of the body; self-mutilation at the site of pain or close by.
CHANGES IN ACTIVITY LEVEL they want shorter walks or avoid walks; restlessness; avoiding contact with humans and other animals or seeking more affection; inability to focus or learn new things.
FACIAL EXPRESSIONS tense facial muscles with furrowed brows; lips drawn back; a grimace; unfocused eyes; ears flattened back against their head; panting.
POSTURE AND MOVEMENT stiffness when walking; a hunched back; weight bearing is not symmetrical; limping.
COAT CHANGES less shine; changes in direction or texture; moulting; colour changes; dandruff.
SELF-PROTECTION protecting certain areas from contact; not wanting to be helped or picked up; hiding away. SOUND SENSITIVITY musculoskeletal pain has been positively linked with sensitivity to noise in dogs. Fagundes, A., et al. 2018(5) hypothesise that this could be due to the sudden increase in muscle tension, which can occur when a dog is startled by a loud noise that could exacerbate pain.
REACTIVITY growling or barking, avoiding other dogs or people; snapping; lunging when on lead; barking more at stimuli.
Once the dog is in front of the veterinarian, they have numerous skills at their disposal such as observations, clinical history, guardian information and palpation. However, anxiety or fear in the dog can complicate palpation and observations. Just as in humans, the experience of pain can be heightened in anxious animals. This sensitivity may lead to an increased perception of pain and discomfort in our dogs. Recording the concerning behaviour, posture or movement to show the vet can be beneficial in gaining a diagnosis.
Put simply, if we know that a condition is painful in people, we know that it will be painful in animals. Recognising and assessing pain will help with the correct medications being prescribed to people and animals to ensure they are pain free. This is One Medicine, the sharing of information and knowledge between the human and veterinary medical worlds for the benefit of all species.
About the author: Rachel Jackson is the School’s Education Manager at Humanimal Trust. She is a qualified teacher and veterinary physiotherapist, so has a unique understanding of both the education system and animal physiology.
Education Programme: 'Understanding Pain' is also the subject of one of our lessons for post-16 year olds, designed to help them learn about the transformative potential of One Medicine.
References
1. Melzack, R. and Wall, P.D. (1965) Pain mechanisms: A new Theory. Science. 1965; 150:971–9 (https://pubmed.ncbi.nlm.nih.gov/5320816/)
2. Melzack, R. and Casey, K.L. (1968) Sensory, motivational and central control determinants of pain: a new conceptual model. In: The Skin Senses, edited by, Kenshalo, D., Springfield, IL: C.C. Thomas 1968, p. 423-439 Researchgate.net
3. Lauriola, M., Tomai, M., Palma, R., et al. (2019) Intolerance of uncertainty and anxiety-related dispositions predict pain during upper endoscopy. Frontiers in Psychology 10: 1112.
4. Philips. H.C. (1988) The Psychological Management of Chronic Pain: A Treatment Manual. New York: Springer.
5. Lopes Fagundes, A.L., Hewison, L., McPeake, K.J., Zulch, H., & Mills, D. (2018). Noise Sensitivities in Dogs: An Exploration of Signs in Dogs with and without Musculoskeletal Pain Using Qualitative Content Analysis. Frontiers in Veterinary.