There are sensory and emotional aspects of pain, and, as such, every individual can experience pain differently (Monteiro et al., 2022). Pain is not the same as nociception (the processing of noxious stimuli) but a multidimensional experience encompassing several different factors (IASP, 2023). Pain perception (ie the conscious processing of pain) can be exacerbated by protective (negative) emotions experienced due to environmental and social stressors and vice versa (Self, 2019). This can be a vicious cycle, especially for cats, who can become easily distressed in an unfamiliar environment such as the veterinary clinic.
The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage” (IASP, 2023).
Pain is thought to have an adaptive function that helps the affected individual protect themselves, recover from injury and illness, and ultimately survive. However, pain can also be maladaptive, wherein it serves no purpose, has no obvious endpoint and negatively impacts quality of life (Monteiro et al., 2022).
Pain can be split into three domains (Steagall and Monteiro, 2018; Talbot et al., 2019):
- Sensory-discriminative – determines the site, intensity and duration of pain
- Affective-motivational – the unpleasantness and emotional consequence of pain, causing the animal to take protective action
- Cognitive-evaluative – an individual’s current experience of pain based on previous experience and knowledge. This domain of pain is challenging to assess in animals as they are non-verbal
Pain is often classified as either adaptive (acute), where there is a sudden onset of pain that is self-limiting and stops once damaged tissue is fully healed, or conversely, maladaptive, or “chronic”, pain, which persists for longer than expected or than what is considered normal (Monteiro et al., 2022). However, it is worth noting that some patients affected by chronic pain will also experience episodes of acute breakthrough pain, too.
Challenges of assessing pain in cats
Cats are programmed as prey animals, predators and self-sufficient survivalists, so mask pain or illness as a survival strategy (Ellis, 2018). They can be difficult to assess for pain in a veterinary environment, where they feel under threat due to the unfamiliarity of their surroundings and the stressors present (Steagall et al., 2022). Furthermore, cats may have already established a negative association with being in the veterinary environment if cat-friendly measures have not been put in place during previous visits.
[Cats] can be difficult to assess for pain in a veterinary environment, where they feel under threat due to the unfamiliarity of their surroundings and the stressors present
Fearful or anxious cats may try to hide or freeze, avoiding interactions with veterinary staff altogether. They might also display repulsion behaviours such as hissing, swiping or biting when approached or handled, especially if previous attempts to avoid unwanted interactions have been unsuccessful (Ellis, 2018). These behaviours may occur whether a cat is in pain or not, and this, coupled with the fact that cats have a limited repertoire for social communication with people, makes them challenging to read.
Other factors, such as the cat’s temperament, certain medications and staff training on pain assessment, can also influence the effectiveness of pain assessment in cats (Evangelista et al., 2019; Steagall et al., 2022).
Pain assessment in cats – where are we now?
Assessment and management of pain in cats have improved dramatically over recent years (Steagall et al., 2022). Validated pain scoring systems help to prevent subjectivity and reduce the incidence of observer bias when assessing cats for signs of pain (Monteiro et al., 2022). Validated pain scoring systems are now available for acute and chronic pain, and veterinary nurses play a crucial role in recognising and assessing pain in feline patients.
Validated pain scoring systems are now available for acute and chronic pain, and veterinary nurses play a crucial role in recognising and assessing pain in feline patients
Alongside a physical examination and nutritional assessment, a pain assessment should be part of every examination (Steagall et al., 2022). Moreover, cat owners can also be given the information and tools to pain score their cats at home, where assessment might be more accurate due to the cat being more relaxed.
Assessing acute pain
Validated pain scoring systems used to measure acute pain in cats include the UNESP-Botucatu Multidimensional Composite Pain Scale, the Glasgow Composite Pain Scale and the Feline Grimace Scale (Steagall et al., 2022).
There are advantages and disadvantages of each pain scoring system; however, the Feline Grimace Scale is particularly useful for measuring acute pain in cats as it does not require the assessor to touch the patient. Instead, it relies on a 30-second observation and assessment of five action units, including:
- Ear position
- Orbital tightening
- Muzzle tension
- Whisker position
- Head position
Each action unit is scored at 0 (absent), 1 (moderate) or 2 (obviously present). Analgesia should be considered where the cut-off value is four or more, as cats scoring this high will be experiencing pain (Evangelista et al., 2019).
The Feline Grimace Scale is reliable to use in cats that have undergone various procedures, including dental extractions (Watanabe et al., 2020). Training on how to use this pain scoring system and examples of scoring in real time are available via the Feline Grimace Scale website and app, making it easy and accessible for all to use.
A recent study has shown that deep neural networks and machine learning models can be used predict facial landmark positions and pain scores using the Feline Grimace Scale on smartphones, making assessment of acute pain in cats even more reliable and accessible (Steagall et al., 2023).
Physiological changes, such as increased heart and respiratory rates, can occur in cats experiencing acute pain. However, these changes can also occur in distressed cats or those being treated with certain medications or suffering from non-painful illnesses, so physical indicators should be considered when evaluating patients as a whole but not for pain assessment alone (Steagall and Monteiro, 2018).
Elevated blood pressure has been linked with an increase in cortisol concentrations and pain in cats, so may be a more reliable indicator of pain
Elevated blood pressure has been linked with an increase in cortisol concentrations and pain in cats, so may be a more reliable indicator of pain, but some cats do not tolerate having their blood pressure measured, especially if they are uncomfortable or stressed during hospitalisation (Smith et al., 1996; Steagall and Monteiro, 2018).
Body language, posture and behaviour
Although several factors can influence a cat’s body language, posture and behaviour, pain may also be present if the following signs are observed (Merola and Mills, 2016; Steagall et al., 2022):
- Hunched body posture (abdominal pain)
- Flank muscle contraction (abdominal pain)
- Hyporexia or anorexia
- Vocalisations such as hissing, growling and groaning
- Restlessness and irritation
- Blepharospasm (eye disease/trauma)
Caregivers may report behavioural changes such as their cat being withdrawn and/or hiding in unusual places, a cessation of normal behaviours (scratching, grooming, playing, exploring, etc), reduced interaction with people or other animals in the household, and a lower tolerance of being touched. Veterinary professionals may observe wound interference and anorexia in painful hospitalised cats or notice head shaking in cats experiencing dental pain (Steagall et al., 2022).
Assessing chronic pain
Ageing cats are more likely to suffer from ongoing diseases that lead to chronic pain (Monteiro and Steagall, 2019). Changes in behaviour due to chronic pain are gradual in cats, and caregivers may not notice subtle changes or will assume they are part of the normal ageing process. This can have a detrimental effect on feline welfare, especially as both periodontal disease and osteoarthritis are common but painful conditions in cats (O’Neill et al., 2023).
Changes in behaviour due to chronic pain are gradual in cats, and caregivers may not notice subtle changes or will assume they are part of the normal ageing process
Other conditions such as chronic kidney disease, feline idiopathic cystitis, gastrointestinal disease, skin disease, ophthalmic disease, neurological conditions and neoplasia may also cause chronic pain in cats (Monteiro and Steagall, 2019).
Behaviour and movement
Behavioural changes in cats with osteoarthritis or degenerative joint disease can be difficult for caregivers to notice as they are so gradual and multiple limbs are often affected, meaning obvious lameness is not present (Epstein et al., 2015). The behaviour of affected cats will slowly change so they spend less time outside, playing or hunting, grooming and scratching (especially of vertical surfaces), and avoid using the stairs (Monteiro and Steagall, 2019). Cats with osteoarthritis may also be more likely to house soil and favour lower resting areas due to impaired mobility. However, these signs may occur due to other health or behaviour problems.
One study by Enomoto et al. (2020) pinpointed six key indicators of pain caused by degenerative joint disease in cats:
- Jumping up
- Jumping down
- Climbing up stairs
- Climbing down stairs
- Running normally
- Chasing moving objects
Although cats can show several signs of joint pain, these indicators were the most prominent in cats affected by degenerative joint disease. Therefore, they could be useful for veterinary professionals to work through with owners when assessing cats with mobility issues.
The Feline Musculoskeletal Pain Index was developed by the NC State University’s College of Veterinary Medicine and is a validated tool for measuring musculoskeletal pain in cats (Enomoto et al., 2021). The questionnaire can be accessed via the Pain Free Cats website and can be used to help assess and monitor cats who may suffer from musculoskeletal pain.
Although cats are genetically programmed to hide signs of pain, there are now several ways to assess cats suffering from acute and chronic pain. Caregivers may not recognise the link between changes in their cat’s behaviour and pain, so veterinary professionals can explain why these changes occur and work with caregivers to manage their cat’s pain and improve their quality of life.