What is pain?

We all have experiences of pain in our lives, whether it is major or minor, short-term or chronic. Pain can be hard to define however, because it is such a common experience. The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage.” That definition means that sometimes there is injury or damage (for example a cut, a broken bone, etc.), and sometimes there is no injury, but it feels like it (a “stabbing” headache). Pain is the body’s alarm system, not unlike a smoke alarm. It is a basic signal and tells us when something is wrong and needs attention. It is not designed to be very good at locating the nature of the problem, or even telling us how big it is, and it was meant to be turned on for only short periods of time.

Pain, at a biological level, is expressed along many pathways. There are rapid-firing nerve endings that give us the first signal of pain (nociceptive pain); an example is touching a hot stove. There is the “inflammatory soup” of the many chemicals and cell types that respond to injury as part of alarm and then healing response. This response is painful, and includes other parts of healing such as swelling, redness and warmth (inflammatory pain). When nerves are affected directly, perhaps from a neuron disease, they can send pain signals without any other stimulus, often electrical feeling (neuropathic pain). Finally, the brain itself can generate the feeling of pain, even in absence of injury or tissue damage elsewhere - the neurons set off a false alarm that persists. Some clinicians say that this is one type of neuropathic pain as it still involves nerves, but others call this ‘central pain’, a term we prefer. Of the 4 types of pain, we know the least about this central pain because it is very hard to study.

Pain is the most common symptom reported by parents and caregivers of children with severe neurological impairment (SNI) and is seen in up to 42% of children on a daily basis. Pain is notoriously difficult to identify, and therefore treat, in non-verbal children because their signals of distress are ambiguous and hard to decode. Parents and healthcare providers rely on interpretation of “pain-like behaviours” (vocalizations, grimacing, arching and muscle tightening, etc.) to determine the presence of pain. These signs are challenging to evaluate and the pain cannot always be attributed to a specific cause. Moreover, in children with complex neurological conditions, pain-like behaviours are not always due to disease or injury, but instead may be due to generalized irritability of the central nervous system (central pain as described above). It is this kind of sensation that we call Pain and Irritability of Unknown Origin (PIUO).

Lacking an explanation for the source of pain leaves clinicians unable to treat it and increases a parent’s obstacles in providing care. Much is known about the assessment and treatment of both acute and chronic pain in typically developing children, from neonates to adolescents. While the treatment for an individual patient might pose significant clinical challenges (e.g. treating cancer pain in a toddler), the outlines of what to search for, the likely sources, and the starting points for treatment are clear. Children with SNI have marked differences in their nervous system because of differences in brain anatomy, injury to the developing brain, disruptions in healthy cell metabolism, or a host of other disruptions. Since we cannot make the same assumptions and inferences about pain signals or responses as we might in the typical child, we need better tools to address pain in these children.