Millions of Americans live with chronic pain, particularly an aching lower back, but doctors have so far not been able to measure just how much their patients hurt.
Researchers have now edged closer to having a tool that can help quantify the intensity of chronic pain and track it through the course of treatment -- rather than relying on the crude scale that asks patients to rate their pain from 1 to 10. The problem has always been that one patient's 10 may be another patient's 1.
Low back pain is the second-most common neurological ailment after headaches in the United States. The depression, impaired memory and attention and diminished quality of life associated with chronic lower back pain exact a huge psychological and economic toll, making it an important target for study.
A technique called arterial spin labeling, performed during MRI scans, allowed scientists at Brigham and Women's Hospital in Boston to observe changes in blood flow to specific regions of the brain as chronic back pain patients held uncomfortable positions inside the scanner. As the patients' brains were registering the distressing sensation, the investigators watched blood flow activate or "light up" different regions. They could then measure that blood flow during those painful episodes.
"Normally, when you do studies with older techniques, you're not able to track the changes in people's chronic pain over time," said Dr. Ajay D. Wasan, an assistant professor of anesthesiology and psychiatry at the Brigham and Women's Hospital and Harvard Medical School, who led the study with his postdoctoral fellow Marco Loggia. "This provides a way to look at the physiology of the brain when someone has more or less chronic pain."
Wasan and Loggia studied 32 patients, mostly women who had an average age of 47, half of whom suffered from chronic low back pain or pain radiating down the legs that they'd endured more than five years. The others were healthy comparison subjects.
When researchers applied heat to the skin of all 32 subjects, brain scans using the new imaging technique found that both healthy and chronic pain patients processed the sensation the same way, without lasting effects. However, when researchers put all study participants through maneuvers meant to induce pain in those with pre-existing back or leg pain, the brains of patients with chronic low back pain processed painful stimuli differently than the brains of healthy subjects, according to findings published in the August issue of the journal Anesthesiology, which earlier appeared online.
When chronic pain patients raised their straightened legs to an uncomfortable angle for 10 seconds, or performed an uncomfortable pelvic tilt, their pain worsened by an average of 34.3 percent and only slowly subsided, Wasan told ABCNews.com. In contrast, healthy patients reported no pain during the maneuvers.
Among the chronic pain patients, tasks that ratcheted up their pain activated brain areas known to process pain, including areas involved in paying attention to important stimuli, Wasan said. "We know attention is really important to pain, so drugs that might change a person's ability to pay attention to their pain or be distracted from their pain certainly are possibilities down the road," he said. "The technology certainly needs to be developed more and researched more before we get to that point."
Ultimately, he said, "as we understand the network involved in processing pain, we hope we can use that to lead to more targeted treatment that will change the functioning of specific areas of the brain." Brain scans might determine who is likely to respond to particular treatments and also be used to monitor treatment effectiveness, he said.
Colleagues in the pain treatment community were largely impressed by the quality of Wasan's research but said it was still early.
"If this were a board game, this is three steps down the Chutes and Ladders with thousands of steps to go," said Dr. Perry G. Fine, a pain specialist at the University of Utah in Salt Lake City. "You never get anywhere unless you take the first step. It's a really important step."
He said the brain imaging technique "allows for us to understand how chronic pain differs from acute pain. You see parts of the brain light up where there's increased neural activity that normal people don't have and probably cannot begin to express or imagine."
"Pain is still as complicated as it's ever been," he said. Having a tool to observe brain activity during chronic pain means doctors "can now have a bit more trust and believe in what the patient says" when they describe their pain. However, he cautioned that economic and other factors leave physicians a long way from "being able to put everyone in a scanner."
While praising Wasan's research as well-planned and well-executed, and saying it provided "a valuable tool in gaining information about processes in the brain," Dr. Alex Cahana, chief of the division of pain medicine at the University of Washington in Seattle, also found it problematic.
"It perpetuates the idea that we need to look at imaging in order to validate pain," said Cahana, an anesthesiologist who uses a combination of pills, injections, motivational interviews and guidance to help patients live a happier life with their pain. "At the end of the day, the imaging of pain … does not explain to us a cause of pain. It doesn't explain why the pain is chronic."