Chronic pain refers to a pain condition that occurs over a long period (months) and can be considered maladaptive. It has been increasingly recognised that chronic pain is a condition that can affect companion animals, but there is a lack of reliable and accurate methods for detecting it in pets. This review article from the USA summarises the current state of knowledge surrounding the measurement of chronic pain in cats and dogs.
Animals cannot verbalise the magnitude of their pain, consequently, researchers must rely on direct and indirect indicators of pain to assess its severity. Direct indicators of pain can include changes in physical activity levels. Indirect indicators can include central sensitisation of the pain response; meaning that chronic pain can increase the pain response that an animal shows to other sources of pain, such as electrical stimulation. All measures of chronic pain should be scientifically validated to ensure reliability.
Sources of chronic pain in cats and dogs
- joint pain – chronic joint pain can be indicated by changes in activity levels, and these changes can be objectively measured using wearable activity trackers. However, these results will vary with the size and shape of the animal, and the degree of change in activity that is needed to indicate a clinically relevant change in pain severity has not yet been determined. Measuring the pain response of animals to additional painful stimulation, such as a mild electric shock, is a possible avenue of research for identifying chronic pain, but there is no standard methodology for this measure that allows comparison between studies.
- cancer pain – Cancer pain is a poorly studied and unique pain state that can result from the growth of the primary tumour, the associated changes in immune function, or the side effects of treatments such as radiation.
- neuropathic pain – Neuropathic (nerve) pain is recognised as a chronic condition, but very little research has been conducted on measuring this state in pets.
In conclusion, while some progress has been made in assessing chronic pain in cats and dogs, there is considerable interest in improving this aspect of veterinary science.
Lascelles BDX et al (2019) Measurement of chronic pain in companion animals: Discussions from the Pain in Animals Workshop (PAW) 2017. The Veterinary Journal 250:71-78.