New back pain research
Patients with lower back pain that can’t be traced to a specific physical cause may have abnormal pain-processing pathways in their brains, according to a new study led by University of Michigan researchers.
The effect, which as yet has no explanation, is similar to an altered pain perception effect in fibromyalgia patients recently reported by the same research team.
In fact, the study finds, people with lower back pain say they feel severe pain, and have measurable pain signals in their brains, from a gentle finger squeeze that barely feels unpleasant to people without lower back pain. People with fibromyalgia felt about the same pain from a squeeze of the same intensity.
But the squeeze’s force must be increased sharply to cause healthy people to feel the same level of pain – and their pain signals register p in different brain areas. The results may help lead researchers to important findings on lower back pain, and on enhanced pain perception in general.
Senior authors Richard Gracely, Ph.D., and Daniel Clauw, M.D., did the study at Georgetown University Medical Center and the National Institutes of Health, but are now continuing the work at the University of Michigan Health System.
To correlate subjective pain sensation with objective views of brain signals, the researchers used a super-fast form of MRI brain imaging, called functional MRI or fMRI. They looked at the brains of 15 people with lower back pain whose body scans showed no mechanical cause, such as a ruptured disk, for their pain. They also looked at 15 fibromyalgia patients and 15 normal control subjects
As a result, they say, the study offers the first objective method for corroborating what lower back pain patients report they feel, and what’s going on in their brains at the precise moment they feel it. And, it continues to give researchers a road map of the areas of the brain that are most – and least – active when patients feel pain. The researchers hope that further study on larger groups of patients will yield more information on altered pain processing.
‘The fMRI technology gave us a unique opportunity to look at the neurobiology underlying tenderness, which is a hallmark of both lower back pain and fibromyalgia,’ says Dr Clauw. ‘These results, combined with other work done by our group and others, have convinced us that some pathologic process is making these patients more sensitive. For some reason, still unknown, there’s a neurobiological amplification of their pain signals.’
Much of the pain may be due to pulled muscles, strained ligaments, damaged joints or small tears in the disks that act as cushions between the bones of the spine – all causes that don’t show up well on X-rays but often can be seen on CT or conventional MRI scans. These physical causes often disappear after a few weeks, but many patients have chronic or recurring lower-back pain.
In the study, the lower-back pain patients were examined by CT scan to rule out mechanical causes of their pain. Then they, the fibromyalgia patients and the healthy control subjects had their brains scanned by fMRI for more than 10 minutes while a small, piston-controlled device applied precisely calibrated, rapidly pulsing pressure to the base of their left thumbnail. The pressures were varied over time, using painful and non-painful levels that had been set for each patient prior to the scan.
The study’s design gave two opportunities to compare patients and controls. The subjective comparison measured the pressure levels at which the pain rating given by back pain patients, fibromyalgia patients and control subjects was the same. The objective comparison looked at the rating that the three types of participants gave when the same level of pressure was applied.
The researchers found that it only took a mild pressure to produce self-reported feelings of pain in the lower-back pain and fibromyalgia patients, while the control subjects tolerated the same pressure with little pain.
“In both the back pain patients and the fibromyalgia patients, that same
