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ANY SUFFERING from pain (see Pain-Brain Connection)—acute or chronic—can be compounded by an inability to convince medical personnel how much it really hurts. Now research has found that an individual’s genes help determine how intensely they respond to pain—as well as how their body metabolizes different pain relief medications. Eventually genetic testing could provide information about an individual’s pain tolerance level as a supplement to their subjective descriptions of pain.
Individual responses to pain depend on an interaction of environmental and innate factors. Race and ethnicity make a difference (African Americans and non-Caucasian Hispanics report more pain than Caucasians) as does gender, with women typically reporting more pain than men. But mice studies have suggested that up to 76 percent of the variance in pain response could be due to genetic differences, according to the Journal of Medical Genetics.
A recent study of more than 2,700 people, who were all experiencing chronic pain serious enough to be prescribed opioid drugs, found different genes more prevalent in each of three groups. Compared to people with high pain perception (who rated their pain seven to 10 on a 10-point scale), one gene was 33 percent more prevalent among those who rated their pain as low (one to three on the scale). Two other genes were more prevalent among those who rated their pain as moderate (four to six). And among those “high-perceivers,” a fourth gene was 25 percent more common compared to those with moderate pain. The research was presented by Tobore Onojjighofia at Proove Biosciences at the 2014 American Academy of Neurology meeting.
Approximately one-third of the U.S. population—about 100 million people—suffers from chronic pain, defined as the perception of pain persisting for longer than three to six months. But a clinically acceptable response to treatment is currently only 30 percent pain reduction, which many physicians agree is unacceptable. Also, some 70 percent of those with chronic pain, despite taking pain medication, continue to experience “breakthrough” pain flares.
Currently the process of finding the best opioid for an individual patient is based on trial and error because of the fine line between pain relief and toxicity. More than 2.2 billion “adverse drug effects” occur annually, with 100,000 cases resulting in death. (Genetic testing could also provide information to help with the selection of antidepressants.)
Although still not widespread, “pharmacogenetics testing” is already being used by physicians to get patients onto safer and more effective medications, Lynn Webster, Salt Lake City pain specialist and past president of the American Academy of Pain Medicine, told a panel of pain experts assembled last January by Pain Medicine News.
Several existing genetic tests include “Pain Medication DNA Insight,” offered by Pathway Genomics Corporation in San Diego, Calif.; and “Genetic Testing for Personalized Pain Management” by AI Biotech in Richmond, Va. The AI Biotech site states “prescribers can now personalize drug therapy by identifying patients’ drug metabolizing phenotypes for improved efficacy and reduced adverse drug effects.”
Genetic testing will have two major clinical impacts, Luda Diatchenko of McGill University told the panel. First, to help patients who are deciding whether to have elective surgery— because those undergoing even minimally invasive surgery have up to a 50 percent chance of developing chronic pain that lasts more than six months. Second is the “strong potential for clinical classification of chronic pain patients” that can help with drug treatment choice.
As for predicting the risk of addiction, Dr. Webster believes that more data and large trials are needed. But another panel member, Anita Gupta, associate anesthesiology professor at Drexel University, cited “emerging clinical research” that suggests this will be possible “in the near future.”
Dr. Webster ended the panel with the hope “that clinicians will routinely have … evidence-based genetic information to guide individualized care…. Pharmacogenetic testing should inform clinicians about the best treatment options with the least adverse-effect probability.”
Until genetic testing is more widely available, however, people can improve the way they report pain. “I ask people to remember the worst pain they’ve ever experienced in their lives,” says Seddon Savage, incoming president of the American Pain Society. “That level of pain becomes the benchmark to which we compare the current pain.”
Savage also suggests evaluating pain over a period of a week, and then assigning a number to the pain at its most severe, least severe and most typical level. In addition, she says, “Your doctor needs to know not just how much the pain hurts, but how the pain hurts.” Tissue injury, like a back injured while shoveling snow, is usually a dull ache; nerve pain, which has many causes, is often described as shooting, buzzing or burning.
Descriptive “pain scales” can be taken to the doctor to help pinpoint where your pain falls. One, created by Karen Lee Richards for ChronicPainConnection, divides the 10 pain levels into three sections with specific criteria described for each: “mild” ranges from barely noticeable (one) to distracting but you can adapt (three); “moderate” ranges from distracting (four) to interfering with daily activities (six); and “severe” ranges from limiting daily activities (seven) to “crying out and/or moaning uncontrollably” (nine). Ten is “unspeakable,” but “very few people will ever experience this level,” Richards says.
I try to imagine how these possibilities might have affected my only visit to the ER for pain at the crying-out-and-moaning level: Would things have gone better with Richards’s scale on hand or a genetic test defining me as a low-perceiver? I suspect that depends on the medical personnel. By the time I saw a doctor, her only question to me was: Could you be depressed? No, but I was furious. Fortunately, I’d already begun treatment for Lyme Disease and, over the following weeks, the pain slowly subsided.
—Mary Carpenter