Shingles and toying around with the definition of pain

Yesterday I learned from my family doctor that the dormant Herpes Zoster virus that reside in my dorsal root ganglia have for some reason opted to awaken and infect what I believe is my 10th or 11th thoracic nerve.  In other words, I’ve got shingles.

So what does an academic with special interest in pain do when he gets shingles?  As it turns out, think was too much about the experience.  I’m going to get a colleague of mine to run a few tests, see how my pressure and cold pain thresholds are in the area and in remote areas, and see what we can sort out.  I’ve already completed an SLANSS of course, and I currently score a 6 out of 24, fortunate that the sensation is not really painful yet, more itchy and slightly allodynic.  According to my SLANSS score however, I am happily not experiencing pain of primarily neuropathic origin, which would be best indicated by a score of 12 or higher.  However, the experience has been getting a bit more intense over the past 24 hours, so perhaps I’ll complete it again tomorrow and see if things have changed.

This experience reminds me of a blog post I made years ago on a blog that as far as I know no longer exists, lost somewhere in the ether of the internet.  This pertains to the current IASP definition of pain, initially coined by psychiatrist Dr. Harold Merskey, as: ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’  This definition is very elegant and has informed any number of pain assessment tools since its description.  I am extremely fortunate to have had the chance to sit and chat with Dr. Merskey on more than one occasion, as he and I live only blocks from one another.  He is a brilliant man, has a remarkable brain for pain, and someone that I deeply respect.  So when I raise this next point about a possible tweak in the definition of pain based on my current personal experience and years of dealing with people in pain, it is out of no disrespect to Dr. Merskey.  You might consider it little more than mental masturbation, simply a thought that I feel compelled to record.  In fact I will invite his comments on this post.

I am currently experiencing an unpleasant sensory and emotional feeling, and it is clearly associated with tissue damage (viral nerve infection), so on these levels what I’m feeling fits the definition of pain.  But I’m not feeling pain, or perhaps more accurately, the experience is not currently being perceived as painful.  I would describe it more as itchiness with occasional bouts of mild discomfort.  So while I fit the definition, my personal experience isn’t jiving with what I should be feeling by definition.  Now, I’ll be the first to recognize that no definition of anything is going to be all-encompassing, there will always be occurrences that do not fit the definition, so again this is not meant to be a criticism in any way of the definition of pain.  That said, I’ve been giving some thought to how the definition could be tweaked to better discriminate between pain and what I’m currently feeling.  Here’s what I’ve come up with so far:

“An intense sensory and distressing emotional experience associated with actual or potential tissue damage, or described in terms of such damage, that strongly motivates behavior to restore of homeostasis.”

Here's my thinking on this.  Keep in mind that we're discussing an output, the end result of scrutiny of a variety (perhaps countless) inputs.  I also fashioned this definition from the framework of Melzack's Neuromatrix model, suggesting that pain has sensory-discriminative, cognitive-evaluative, and motivational-affective components.

'An intense sensory...experience', got the sensory-discriminative part covered there.  It's a sensory experience, and intense enough to demand attention, discriminating it from a mild sensory experience.

'associated with actual or potential tissue damage, or described in terms of such damage', the cognitive-evaluative component - 'pain' will be the outcome only if the organism perceives that it's under threat.

Notice that I've separated the word 'unpleasant' into intense (sensory) and distressing (emotional).  I'm not entirely sure I'm right on this one though.  My feeling is that we can't assign an emotional experience (unpleasantness) to a purely sensory experience, which would be more appropriately described in terms of intensity, frequency, location, quality and the such.  But I can also see an argument against this stance, and would be OK with returning the 'unpleasant' term.  Would be interested in hearing the opinions of others.


I've chosen the word 'distressing' intentionally, based on my own personal position that the distinction between a 'hurt' and a 'pain' is the degree to which the sufferer feels threatened by the experience - its predictability, controllability, understanding of causation and temporality, etc...


Finally, I've hesitantly added a small additional bit at the end, the motivational bit.  This is partly pulled from Melzack's conceptualization of chronic pain as an inability of the organism to return to a state of homeostasis.  If we conceptualize pain as an aversive response to a perceived threat - which incidentally can also describe fear and anxiety, hence the tissue damage requirement - then it seems to me that the experience of pain should be defined by a desire to either withdraw from the stimulus, withdraw from the environment, seek care or support, or engage in other coping behaviours aimed at returning to a level of perceived 'safety'.


So within this refined definition, I would describe the experience I'm currently having thanks to my shingles as intense, but not necessarily distressing.  It's associated with tissue damage, but on the other hand it's not currently demanding that I withdraw or change my behaviour (with the possible exception of a bit more scratching than usual).  So by this tweaked definition, what I’m feeling doesn’t fit the definition of pain, which seems to work at least in my case.


So, what do y'all think?  I'd love to get your comments on this.