Saturday, May 18, 2013

Melzack and Katz, Pain. Part 3c: Pain depends on everything ever experienced by an individual

The paper, Pain.

Part 1 First two sentences
Part 2 Pain is personal
Part 3a Pain is more than sensation: Backdrop
Part 3b Pain is not receptor stimulation

The next sentence in the abstract is,
"Rather, injury or disease produces neural signals that enter an active nervous system that (in the adult organism) is the substrate of past experience, culture, and a host of other environmental and personal factors."
Please see Part 3b for my personal take on that... but it's not just my opinion..

There is ample support in our profession for the whole idea of a human organism being an accretion of experience through time than just me: Butler. Moseley. Thacker. Gifford. Just a few! Hundreds more. Possibly thousands. Don't everybody all shout at once. 

On second thought, heck - why not? 

Everybody together now!!! What do we want? 
Better pain theory taught at the undergrad level!! 

When do we want it? 
Thirty years ago!! 


In 1998, a remarkable UK PT, Louis Gifford, who subsequently published a remarkable, brilliant series of books on pain, wrote a paper (well, he has written lots of papers, but this one is pivotal in my opinion). Here is the abstract:
Gifford L, Pain, the Tissues and the Nervous System: A conceptual modelPhysiotherapy Jan1998, 84:1 27-37
Summary: This paper challenges current clinical models and systems for assessing and managing on-going pain states to incorporate a broader biological and therapeutic framework. Included is an acceptance of the current criticisms made towards a purely tissue based/modality based paradigm for pain treatment. The mature organism model proposed is presented as a workable conceptual starting block for incorporating mechanisms of pain into the broad science of stress biology and the biopsychosocial model of pain.
Gifford's mature organism model (MOM) for PT

In this paper, Gifford wrote that he wanted to help clinicians link together complex issues and mechanisms involved in pain problems, help them see the inadequacy of current approaches, and provide a new pain model. Basically he wanted PTs to start using our brains and get away from ritualistic superficial location-specific modality treatment. He said, "Physiotherapists are being bluntly urged to change their approaches and rationales."

Bluntly! Did we "get it"? Apparently not everybody, and not the schools. Not all at once, and not very evenly. 
He described "the mature organism model (MOM)," which he had taught for many years, in which he argued pain was based on biological stress response. 
"the sensation of pain is seen as a perceptual component of the stress response whose prime adaptive purpose is to alter our behaviour in order to enhance the processes of recovery and chances of survival."

Gifford, with zoology degree from his life before PT, held that the body was gene carrier, and the CNS a "stress response coordination center" that 
"continually samples few innate but vital sample-scrutinise-action (consciously and ‘unconsciously’) the outside environment, its own body and relevant past experiences (the brain samples from ‘itself') - and then ‘outputs’, or responds on what it finds to the best advantage for its body and the vital genes it contains."

Output consisted of behaviour and physiology, expressed through systems:
  • somatic motor 
  • ANS (sympathetic, parasympathetic, enteric)
  • neuroendocrine 
  • immune 
Maturation involved learning from successes from behaviours that resulted in surviving. Excellent proposition. I concur completely. 

One could say that pain is a learned behaviour. 

From Melzack and Katz once again, the next sentence of their abstract: 
"These brain processes actively participate in the selection, abstraction, and synthesis of information from the total sensory input."
Yes they do. They certainly do. 
Like learning to ride a bike. Once the brain has learned how to do that, it doesn't forget. There is some sort of implicit learning that goes on in there, about mounting a pain defense. 
The next sentence:
"Pain is not simply the end product of a linear sensory transmission system; it is a dynamic process that involves continuous interactions among complex ascending and descending systems."

Hmmnn.. I suppose that's the story for most kinds of pain in most people. I'm sure Melzack himself would argue against this statement as being the last word, because as his own research showed, there can be pain of the utmost nasty kind, continuously or intermittently or spontaneously generated in the complete absence of ascending systems altogether, i.e., when previously existing ascending systems became disrupted, even deliberately obliterated. 

I now have obtained and read the paper cited in Part 1 of this series,  Melzack R, Loeser JD. Phantom body pain in paraplegics: evidence for a central ‘‘pattern generating mechanism’’ for pain. Pain 1978, 4:195 – 210. 

Here is the introduction:
Phantom body pain in paraplegic patients is the most mysterious of all pain phenomena. It has been traditionally assumed [45] that the essential cause of pain in any part of the body is activity in the receptor-fiber units that innervate it. In this paper, however, we shall describe paraplegic patients who had undergone removal of an entire section of the spinal cord (segmental cordectomy) in the attempt to alleviate phantom body pain, yet they still suffered severe pain in the denervated areas of the body. There is no reason to believe that the pain was due to depression or neurosis. Furthermore, the possibility that the pain was produced by nociceptive signals transmitted along the sympathetic chain is ruled out because the pain was not relieved by bilateral sympathetic blocks. The perception of severe, chronic pain in the absence of any input from those parts of the body in which pain is felt has profound implications for theories of pain. The purpose of this paper is to examine the properties of phantom body pains in paraplegics and to propose a theoretical concept to explain them."
My bold. 
This was remarkable, almost 40 years ago, and it's still pretty remarkable today. I mean, think about it. 
The cords were severed, they were not there. The bilateral sympathetic chain as a possible ascending pathway for nociception was not an issue - sympathetic blocks didn't work

The paper describes in depth 5 cases, paraplegics who had severe pain of the most excruciating sort, and continued to have pain no matter how much of their ascending pathways were removed. 

This paper was pivotal, in that it provided one of the four "conclusions" or arguments in favour of Melzack moving on from the strictly labelled line, specificity theory of pain, the same track as everyone else was on (and many are still on), and that he'd been on himself, to consider the human brain in pain from the inside out/ top down instead of only from the outside in/bottom up. It has been cited 318 times in the last 35 years.

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