- Pain is an aversive sensory experience that causes response with protective motor actions, resulting in learned avoidance of the experience.1 In addition to the sensory experience, there is an affective/emotional component.2
- Adaptive pain, which is defined as an appropriate hypersensitive response to a potentially damaging stimulus, is responsive to medication.3
- Maladaptive pain (commonly referred to as wind-up pain), defined as spontaneous hypersensitivity resulting from abnormal processing of a stimulus by the central nervous system (CNS), does not respond to treatment.3
- Allodynia is pain caused by a stimulus that does not normally provoke pain, according to the International Association for the Study of Pain.4 Allodynia can be a component of maladaptive pain.2
- In cats, assessment of pain sensation cannot be determined by measuring plasma cortisol or beta-endorphin concentrations.5
- Heart rate, respiratory rate, body temperature, and response to approaching humans or to stroking cannot be used reliably to determine amount of pain being experienced.5
- Postoperative pain can be assessed by response to palpation, or by a visual or interactive analog scale.5
- Incidence of clinical signs of degenerative joint disease or osteoarthritis in younger cats is estimated to be 34%; incidence in geriatric cats (15 years and older) increases up to 90%. Pain associated with interstitial cystitis may be more prevalent than previously thought because outward signs (eg, urinating outside the litter box) may not always be present.6,7
Causes & Risk Factors
- Acute pain in cats is most commonly associated with trauma or postoperative pain. Other causes (eg, lower urinary tract disease, pancreatitis, inflammatory bowel disease, cholangiohepatitis, pleuritis, upper respiratory tract infections, and obstipation) should be investigated if the cause is not readily apparent.
- Causes of chronic pain are varied but may include degenerative joint disease, dental and gum disease, neoplasia, interstitial cystitis, dermatitis, and chronic wounds.8
- Risks for acute or chronic pain vary according to cause of the pain stimulus, but the risk for chronic pain increases with age.
- Risk for maladaptive pain increases when adaptive pain is not appropriately managed.
Figure 1: Cats in acute pain hold their heads down and squint their eyes, or they may hide their heads. When in a crate or cage, they often have hunched backs and do not move around or respond to humans.
- Maladaptive pain develops when adaptive pain is untreated for a prolonged period, resulting in sensitization of dorsal horn neurons. Maladaptive pain may be present with or following resolution of adaptive pain.
- As the threshold for pain sensation is lowered, wind-up pain develops in both the peripheral and central nervous systems. Pain wind-up can worsen acute pain and cause chronic maladaptive pain.
- Nociceptors throughout the body can convert a chemical, thermal, or mechanical stimulus into an electrical impulse through a process termed transduction. This impulse is transmitted from the periphery to the dorsal horn of the spinal cord, then the brain and thalamus, and finally the cerebral cortex.9
- Hiding or holding head down, squinting the eyes (Figure 1)
- Licking or biting the surgical site
- Hunched back, resisting movement
- Ignoring attempts by humans to interact
- Not urinating (even with a full bladder), eating, or drinking8,10