definition

Uncertainty: perennial controversies in pain understanding


As I write this post today, yet again there are new theories being proposed for that most common of experiences: pain. Not only theoretical controversies, but even the definition of pain is being debated – is pain an “aversive” experience? An aversive sensory and emotional experience typically caused by, or resembling that caused by, actual or potential tissue injury. Some researchers have recently “found” a new nociceptive fibre (though they persist in calling it a “pain fibre” – once again perpetuating the idea that pain is one and the same with nociception).

One of the conversations is whether pain is a sensation, or an emotion, or something else. When I went to University and studied psychology, sensation was defined as “information transmitted by sensory receptors” – in other words, activity in the sensory receptors prior to perception is classified as sensation. Emotions are also defined in psychology, and depending on the theory being followed might be defined as “a complex reaction pattern, involving experiential, behavioral, and physiological elements.” Perception involves recognising and interpreting sensory information, and invokes the idea of awareness as an essential feature. (This is a good place to begin searching for definition – click)

The term aversive indicates “a physiological or emotional response indicating dislike for a stimulus. It is usually accompanied by withdrawal from or avoidance of the objectionable stimulus.” So pain, unlike most sensory experiences also contains an intrinsic element of distaste and avoidance – even people who pursue painful rituals like body suspension will acknowledge that the experience of being pierced is not pleasant but do it to achieve something else, often a feeling of achievement, accomplishment, meeting a challenge. Doesn’t sound too different from people who enjoy running a marathon, or lifting heavy weights.

The new proposed definition also includes the phrase “caused by, or resembling that caused by actual or potential tissue damage” – because we learn to associate the experience we call pain (or whatever word we use in our first language) with what happens when we graze our skin, get pricked by a needle, or knock our shin. For potential tissue damage, think of those staring contests we used to do as kids: who will blink first? Or consider how long we can sit before we’ll move to relieve the numbness-then-ouch on our buttocks! I prefer the term “associate” than “caused by” because we don’t always perceive pain at the time of tissue damage (think about the bruises we find in the morning after a sports game – but we don’t recall exactly how we got them).

So, for what it’s worth, pain isn’t simply a sensation (the experience is always aversive, and invokes an emotion alongside the sensory characteristics) and it’s not simply an emotionit’s a perception, an interpretation of sensory input via nociceptors in the context of current goals (and consequently, attentional focus), social meaning and values, and past experiences (both personal and vicarious). These latter aspects are really important because it’s not uncommon to fail to perceive “ouch” during an important sports game when the attention is elsewhere, and some beautiful experiments have shown that our perception of a potentially painful experience is influenced by what we’re told about the stimulus (Arntz & Claassens, 2004).

The controversies over a definition of pain matter because after the original definition of pain was agreed upon, it was finally possible for researchers, clinicians and commentators to distinguish between the experience and its sensory apparatus. This is important because it enables a focus beyond what goes on in the tissues, to the person’s experience. Prior to defining pain in this way, if a person claimed to have pain but there was no nociceptive activity, he or she was considered lying or mentally unwell. Traces of this attitude continue to this day, sadly.

Focusing on the person’s experience has allowed treatment to shift beyond “issues in the tissues” to help the person deal with what has happened. Even in the absence of current tissue damage and pain, people can continue to be fearful of potential tissue damage and potential pain. Should anyone question this, I usually point out the extraordinary lifestyle changes made by people who have had angina. These people may not be currently experiencing any chest pain at all – but yet protect themselves from the potential of chest pain because “it might happen again.”

A shift away from addressing sensory stimuli towards helping a person who is experiencing pain involves moving away from a biological-only model of disease. We usually call this a biomedical model where what goes on in the body is considered separately from the person who is the subject of “disease”. Of course, this is a straw man argument because biomedical models have been extending to include the person for at least 30 years. Most medical practitioners would want to address the “why has this person fallen and fractured their neck of femur” alongside “fixing the neck of femur fracture with a plate and pin.” But, it troubles me greatly when I hear people say “but what about the bio?” when it comes to incorporating a broad, multifactorial understanding of people experiencing pain into pain rehabilitation. A multifactorial model (call it biopsychosocial if you will) has never negated the biological contributing factors – but has instead placed those factors into relative importance with psychological and social contributions. And psychological and social factors seem to have more to contribute to our experience of pain and resultant disability than, in particular, what happens to a tendon or disc.

And this leads me to the perennial problem of what do we do if pain doesn’t settle, despite our best efforts. This problem is a real and ongoing challenge for both the person experiencing pain, and his or her health. I think it’s a question many health professionals shy away from. Are we afraid we’ve let the person down? Let ourselves down? Failed somehow? What is it like for the person with pain – constantly wondering if this next treatment will do the trick? Or the next? Or whether they’ve failed? Or is it something sinister? There’s no doubt that pain is aversive and it can invade so much of life – but if so much of our experience of pain is related to how we interpret it, what if we were able to re-interpret this experience as less sinister, less distressing?

Health professionals are powerful attitude shapers. Could we use this influence to help people be a little less afraid of pain, and maybe a little more confident that although pain is inherently aversive, humans are infinitely creative and resourceful and can make peace with pain’s presence?

“‘Specialized cutaneous Schwann cells initiate pain sensation”. Abdo H, Calvo-Enrique L, Martinez Lopez J, Song J, Zhang MD, Usoskin D, El Manira A, Adameyko I, Hjerling-Leffler J, Ernfors P.
Science. doi:10.1126/science.aax6452

Arntz A, Claassens L. The meaning of pain influences its experienced intensity. Pain. 2004;109: 20–25. pmid:15082122