Saturday, October 15, 2005

Neuromatrix 3: A Brief History of Pain

In this section, Melzack provides an overview of where pain theory came from and how it has evolved.

Quotes and notes from “A brief History of pain”, Ron Melzack, page 3, Topical Issues in Pain V. 3:
The theory of pain we inherited in the 20th century was proposed by Descartes three centuries earlier.. although humans, Descartes proposed, have a soul (or mind), the human body is nevertheless, a machine, like an animal’s body.

The impact of Descartes’ theory was enormous. The history of experiments on the anatomy and physiology of pain during the first half of this marked by a search for specific pain fibers and pathways and a pain center in the brain. The result was a concept of pain as a specific, straight-through sensory projection system. This rigid anatomy of pain in the 1950s led to attempts to treat severe chronic pain by a variety of neurosurgical lesions.

Decartes’ specificity theory, then, determined the ‘facts’ as they were known up to the middle of (the 20th) century, and even determined therapy.
I made notes from the next few pages:

Specificity theory:
1. injury activates specific pain receptors and fibers
2. these in turn project pain impulses through a spinal pathway to a pain center in the brain
3. felt pain was due to peripheral injury.
4. no room in this theory for psychological contributions to pain (i.e. attention, past experience, the meaning of the situation)
5. pain experience was held to be proportional to peripheral injury
6. back pain in absence of signs of organic disease were labelled and referred to psychiatrists
7. this concept generally failed to help those with severe chronic pain.
8. “To thoughtful observers, specificity theory was clearly wrong.”

Attempts to find a new theory:
1. “Pattern theory”: several different ones, were generally vague and inadequate.
2. “Gate Control Theory”: Came about as the pattern theories evolved.
3. “Goldscheider proposed that central summation in dorsal horns in one of the critical determinants of pain.
4. “Livingston’s theory postulated a reverberatory circuit in the dorsal horns to explain summation, referred pain, and pain that persisted long after healing was completed.”
5. “Noordenbos’s theory proposed that large-diameter fibres inhibited small-diametre fibres.. (also) he suggested that the substantia gelatinosa in the dorsal horn plays a major role in the summation and other dynamic processes described by Livingston.”
6. no explicit role for the brain other than passive receiver of messages, in any of these theories.
7. at least the theories were headed into the spinal cord away from the periphery.

It bothers me no end that my profession continues to exist and operate mostly according to outdated (since the 1950's !) Cartesian theories on pain, especially in the orthopaedic side of it. The orthopaedic branch of the extensive PT profession has generally followed closely behind traditional medical orthopaedic thinking, which is very Cartesian in outlook and practice: In a nutshell, it sounds something like this: If there's pain in the leg, there must be something in the leg that we should cut out, or a joint we should replace, so that it won't hurt the patient anymore. If there's nothing we can see that should be cut out, and the patient still hurts, it must be arthritis, or else the patient must be crazy. Send them to physio.

The physio mentality has been, If there's pain in the leg, something must be weak. If we strengthen it, it will become strong and the pain might go away/ we can wiggle waggle joints, get better movement from them and the pain might go away. If the pain doesn't go away, it wasn't coming from the joints (the patient is crazy) or else I'm not skilled enough (yet) to overcome this person's arthritic pain. Send them back to the doctor.

The orthopaedic theory of pain seems accurate some of the time, and those with their hips replaced or knees replaced are usually pretty happy with the results. But the power of the successes have eclipsed the failures of this way of thinking, this memeplex of ideas. No other sources or mechanisms for pain generation seem to be considered legitimate by this cultural force within healthcare. Lots of middle aged and older people have audibly creaking and clunking joints and are in no particular distress or pain about it. "Arthritis" in the form of joint change shows up on everyone's x-ray sooner or later.. not everyone gets pain. Conversely, lots of young adults have lots of distressing and persistant pain without any x-ray changes. What's wrong with this picture?

Long ago I began exploring soft tissue work. I knew the orthopaedic premise was outright wrong for most peoples' pain, and much too narrow to accommodate either them or me. After having delved into the pain sciences I am beginning to feel vindicated.

No comments: