Saturday, August 28, 2010

Pain - Dispatches from the brave new world of hurt | National Post

Ken Prkachin, a psychologist at the University of Northern British Columbia, knows what pain looks like. His research shows that the facial reaction to pain involves four distinct muscular actions. The eyebrows lower and are drawn in; the muscles around the eye contract, narrowing the eye and producing crow's feet; the muscles in mid-face contract, wrinkling the nose and raising the upper lip; and the eyes often just close.
There are other reactions, such as stretching the lips into a wince, he said, but this appears to be only reliably associated with extreme pain, such as that suffered by soldiers in battle. Even without this detail, he assumed other people knew what pain looked like, too, so he was surprised to discover a constant tendency to underestimate. His test subjects watched video of people in pain, taken at a sports medicine clinic, and consistently pegged it much lower on a number scale than the actual sufferer did.
What he found most "disturbing," though, was that this effect was stronger in health-care workers, suggesting that exposure to pain can dull sympathy. In fact, according to research he is presenting at the 13th World Congress on Pain, which starts today in Montreal, this underestimation can be experimentally induced and strengthened, just by priming people with a few pictures of others in pain.
After that, their judgment skews reliably to the unsympathetic.
"We would have expected that more experience would have made you a better judge," he said.
Pain is a strange thing, unlike any other sensation, and several items up for discussion at the Congress point to its ineffability, and the mental illusions that can bring relief.
Pain is best described in metaphor, such as the broken glass in the throat from a strep infection, or the handyman's vise around the head of a migraine sufferer.
It is awkward to define, although the International Association for Pain Studies, which hosts the meeting of scientists, has made an effort, saying pain is "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage."
Philosophers puzzle over it, this "qualia" that is an irreducible part
of the human experience. It comes in many flavours: sting, ache, throb, burn. It is one of few things that straddles the philosophical distinction between mass nouns and count nouns; you can have some pain, or you can have three pains.
The word itself derives from a Latin root meaning penalty, the association being with pain inflicted as punishment, and it is used as slang for a threat. It seems negative by nature, but it can also be mildly pleasant, such as scratching an itch, sexually attractive as in masochism, or spiritually purifying, as in a marathon or other ascetic rituals.
Pain is subjective, and each of us is its only judge, or the only accurate one at least, given Prof. Prkachin's findings. But as judges, we are easily fooled. Pain is a creation, a communication between nerves and brain that can be disrupted, as in the "thermal grill" illusion, in which interlaced warm and cold stimuli on the skin cause a sensation of burning, or the "mirror treatment" for pain in the "phantom limbs" of amputees, which tricks the brain into believing the amputated limb has been re-created, and feels fine, just like the intact one it actually sees in reflection.
Some theories about why pain evolved seem obvious. Acute pain, such as a bee sting, makes you avoid noxious stimuli. Chronic pain, such as a broken arm, punishes you for moving it and interrupting the healing.
But as Prof. Prkachin describes it, pain also seems to be a system that evolved to let other people know we are suffering, and yet science has ignored its emotional component until only recently.
He calls this a "tragic error," to think pain is just a sense like vision or hearing, unconcerned with thoughts and feelings. How then to explain the research that shows having a doting spouse makes pain seem worse?
An unemotional pain is almost nonsensical. Jeffrey Mogil, a professor of pain studies at McGill University and chair of the Congress's scientific committee, said it would take a very rare type of brain lesion from a stroke to produce one, known as pain asymbolia, in which a person can feel a pain's intensity, but does not seem to mind it.
That is the historical error the IASP definition corrected, by recognizing pain as a fundamentally emotional faculty.
"Ultimately, our response to whatever impinges on our senses is an interpretation by our brain," said Gerald Gebhart, president of the IASP and d irector of the Center for Pain Research at the University of Pittsburgh School of Medicine. "With pain, the interpretation is coloured by past experience, emotional content, gender, genetics, setting in which it occurs."
Smashing your thumb with a hammer might be excruciating, he said, but it will not kill you, and you have no one else to blame, whereas mild chest pains can be emotionally terrifying.
"My sense is that the vast majority of the pain that we experience -- although it's coloured by past experience, and gender and genetics and cultural expectations -- is initiated and driven by some event in the periphery, in the tissue," he said.
That explanation is especially complicated in his field of visceral pain disorders, such as irritable bowel syndrome, which do not have any definite pathological cause.
It is these disorders that are reflected in the curious last clause of the IASP definition. It says pain is associated with not only tissue damage, but potential tissue damage, to reflect the fact that a knife point
In piecing together its impression of the surrounding world, the human brain has a tendency to give priority to vision, said Terry Borsook, PhD candidate in psychology at the University of Toronto.
"What the brain sees, it will believe," he said.
That preference opens the possibility of tricking the brain, of using illusions to relieve certain kinds of pains, from common arthritis to the rare pain in the "phantom limbs" of amputees.
In his presentation on Artificial Feedback Therapy, Mr. Borsook describes "mirror therapy," in which a patient with phantom limb pain lays the intact limb on a mirror and moves it around, while looking at the reflection and imagining it is the amputated one.
By bolstering the imagination's ability to create its own internal reality with the mirror's visual feedback, Mr. Borsook said this creates the "uncanny impression" that the severed limb is resurrected, and feels fine. "That's the magic."
He also describes current experiments on arthritis patients, in which the key step is getting them to attribute their pain to a cause that can be manipulated. To that end, he uses an "augmented reality" system, which is similar to virtual reality except that it uses real life as a backdrop. The arthritis patient watches a live video of himself, on which flames have been superimposed on his painful joints. Once that association is made, the flames are virutally doused, and the patient feels relief.
"We're assisting the person's imagination" he said. THIS WON'T HURT A BIT
University of Montreal PhD student Daniele Laverdure-Dupont is expecting her first child the day after her scheduled presentation about sleep's role in strengthening the placebo effect, so it is possible she will be a last-minute scratch. Nevertheless, her poster describes her CIHR-funded research into this mysterious effect, in which the expectation of relief becomes the cause.
The placebo effect, named for the Latin for "I shall please," has a bit of a bad reputation, because it is deceptive. Ethics boards struggle with proposals to lie to people, to make them expect relief from a sugar pill. So it is hard to study it on truly sick people. Thankfully, lying to healthy undergraduates is much less controversial.
Bunking for the night in a University of Montreal lab, they were told that the device strapped to their arm would get hot enough to cause them pain in the middle of the night, the kind of pain you might rank about a five out of 10.
On the first night, they were given a cream to put on their arm, and told (falsely) it was a proven painkiller. The next night, they got the same cream, and were told it was inert.
As Ms. Laverdure-Dupont explained, the placebo effect works even in sleep. Not only did the expectation of relief from the useless cream make the subjects describe the pain as much less intense the next morning, but they woke up less frequently when the pain was actually happening.
will hurt the skin before piercing it. But neuropathic pain, such as fibromyalgia, does not involve any tissue damage at all, or if it does, it is long since healed, but the pain remains. Therefore, IASP says, pain is also any sensation that is "described in terms of such damage."
The recent history of pain drug development has been poor, Prof. Mogil said, with several promising animal models failing to translate into human applications. Others, such as Vioxx, worked fine but had dangerous side effects.
His research is on the genetic aspects of pain, and he thinks it is only a matter of time before a new pain drug is developed that works only on men or women, reflecting the growing research into sex-specific pain genes.
"I'm more sure than ever that male and females have different pathways to pain," he said. "One day there will be sex-specific drugs."
In the meantime, a bold proposal at this pain conference aims to ease a global inequality in the availability of pain drugs that are already well proven and safe, especially the politically dangerous opioids.
The first global Pain Summit, a meeting of scientists and policymakers, is to take place in Montreal next week, closing the conference with an aim to promote pain management as a universal human right.

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