Some patients wired to feel pain more intensely
Pain management should be individualized
In rehab, you deal with pain on a daily basis. Much of patients’ treatment plans can depend on the level of pain they are experiencing. But how do you know if patients are giving an accurate report of their pain? And why do patients with the same diagnosis sometimes report wildly varying degrees of pain? New research from Wake Forest University Baptist Medical Center in Winston-Salem, NC, confirms for the first time that some individuals genetically are more sensitive to pain than others. The research also shows that patients really are capable of accurately reporting the pain they feel.
"We have all met people who seem very sensitive to pain as well as those who appear to tolerate pain very well," says Robert Coghill, PhD, lead investigator and assistant professor of neurobiology and anatomy at Wake Forest. "Until now, there was no objective evidence that could confirm that these individual differences in pain sensitivity are, in fact, real."
In the study, Coghill and his colleagues used magnetic resonance imaging (MRI) to assess the brain function of 17 healthy volunteers. While their brains were scanned, a computer-controlled heat stimulator heated a small patch of skin on their legs to 120° F, a temperature that most people find painful. The patients’ self-report of the pain, using a scale of 0 to 10, ranged from a low of 1 to a high of almost 9.1
People who reported higher levels of pain showed increased activation in areas of the brain important in the experience of pain. Activation was seen in the primary somatosensory cortex, which perceives the location and intensity of a painful stimulus, and the anterior cingulate cortex, which processes the unpleasant feelings from the pain. There was little difference between subjects in activation of the thalamus, which transmits pain signals from the spinal cord to higher brain regions.
"This difference between cortical and thalamic patterns of activation may help explain pain differences between individuals," he says. "This finding raises the intriguing possibility that incoming painful information is processed by the spinal cord in a generally similar manner. But once the brain gets involved, the experience becomes very different from one individual to the next."
Coghill says his research shows pain management should be done in a highly individualized fashion. "One of the most difficult aspects of treating pain has been having confidence in the accuracy of patients’ self-reports of pain," he says. "These findings confirm that self-reports of pain intensity are highly correlated to brain activation and that self-reports should guide treatment of pain."
The researchers found that the pain scale was a true ratio: If the heat stimulus was turned halfway down, the patients gave half the pain rating, Coghill says.
In addition to the genetic foundation, the variability in the experience of pain also can depend on long-term cognitive factors, such as personality aspects, a past experience with a painful stimulus, or a perception that the stimulus is either positive or negative. For example, a cancer patient likely will feel more negative about pain than a woman giving birth. "The childbirth pain may be just as intense, but it’s not terribly unpleasant because it’s associated with a pleasant outcome," he explains. "The cancer patient is associating the pain with something that is leading to death."
A person with chronic pain likely will become depressed, withdrawn, frustrated, and less physically active, all of which can make the pain seem more intense. "Pain can exact a significant toll on a person’s mental health," Coghill adds. "But just because a patient may be suffering from mental health issues doesn’t mean they are not actually experiencing pain."
So what’s a provider to do? Coghill makes the following recommendations:
1. Use a good, quantitative pain reporting scale that is heavily validated.
Make sure the anchors of the scale are well defined. Don’t just ask patients to rate their pain on a scale from 0 to 10. Define 0 as not at all unpleasant and 10 as the most intense pain imaginable. Or don’t use numbers at all. Coghill recommends the slide algometer manufactured by the Parisian Novelty Co. of Chicago. This $2 plastic slide rule shows the patient a red bar that lengthens as you pull the slider out. On the back, the provider can see the corresponding numbers.
"If you just ask the patient for a number, the pain ratings will cluster around certain numbers. The patient is not going to say his pain is a 6.725. There is also a tendency for patients to stick with one number at each visit rather than changing it," he says. "If you use the visual analog on the slide rule, you get more precision. You might end up seeing a 5.3 vs. a 4.8, which gives you better information."
2. Have the patient separately rate the intensity of the pain vs. the unpleasantness of the pain.
Coghill tells patients to imagine the sound from a radio. The loudness of the music would be the intensity, and other factors such as whether they like what’s playing would be the unpleasantness. "This gives you insight into the impact the pain is having on the patient’s life," he says.
3. Most importantly, recognize that patients are capable of rating pain in a meaningful fashion.
Take them seriously, he says. Coghill illustrates his point about listening to patients with the story of a woman who recently sent him an e-mail about her pain experience after a laminectomy. She said she had a lot of experience dealing with pain and had previously figured out how to remove herself mentally from pain. After the surgery, her physician put her on pain medications that she felt she didn’t need. "She said the post-surgical recovery was awful because of the meds. They took away her own ability to deal with the pain," Coghill says. "A lot of people are suffering unduly because of physician reluctance to prescribe analgesics, but on the other hand, some patients are getting a sledgehammer when they only need a little tap."
Reference
1. Coghill R, et al. Neural correlates of interindividual differences in the subjective experience of pain. Proc Natl Acad Sci U S A 2003; 14:8,538-8,542.
Need more information?
Robert Coghill, PhD, Assistant Professor, Wake Forest University Baptist Medical Center, Department of Neurobiology, Medical Center Blvd., Winston-Salem, NC 27157-1010. Telephone: (336) 716-4284. E-mail: rcoghill@wfubmc.
New research from Wake Forest University Baptist Medical Center in Winston-Salem, NC, confirms for the first time that some individuals genetically are more sensitive to pain than others. The research also shows that patients really are capable of accurately reporting the pain they feel.
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