Scientists say that people who have a certain abnormality in their brain structure are more likely to develop chronic pain following a lower back injury, according to a study published in the journal Pain.
Researchers from the Northwestern University Feinberg School of Medicine say their findings may initiate changes to the way physicians treat patients for pain.
In their study, the researchers were able to identify a "specific irregularity" or "marker" in the axons of the brain.
These are pathways in the brain's white matter that connect brain cells, allowing them to communicate. Some of the axons surround the nucleus accumbens and medial prefrontal cortex. These are two areas of the brain responsible for processing emotion and pain.
The researchers say that the "marker" allowed them to predict patients' persistent back pain with up to 85% accuracy.
Previous research from the team showed that the psychological properties of these two regions can identify which patients will suffer persistent back pain. However, the researchers say that this new study reveals a "pre-existing culprit" for these psychological responses to injury.
Brain irregularities 'trigger vulnerability to pain'
For the study, the researchers conducted MRI scans on 46 patients who had developed a lower back injury within the past 4 weeks, and who had not experienced any back pain in the previous year.
In order for the participants to continue in the study, they had to report a minimum of 5 out of 10 on a pain scale. These patients were then followed for a year.
MRI scans were taken again at the baseline of the study and then again at the end.
After the 1-year follow-up period, around 50% of the patients showed improvements in their back pain, regardless of whether they took anything to treat it.
However, patients who were experiencing persistent back pain showed the same structural abnormality "markers" in their white matter, both at the onset of injury and 1 year later.
A. Vania Apkarian, professor of psychology at Northwestern University Feinburg School of Medicine and senior author of the study, explains:
"The abnormality makes them vulnerable and predisposes them to enhanced emotional learning that then amplifies the pain and makes it more emotionally significant.
We've found the pain is triggered by these irregularities in the brain. We've shown abnormalities in brain structure connections may be enough to push someone to develop chronic pain once they have an injury."
Research may 'reduce burden' of chronic pain in US
According to the researchers, almost 100 million Americans suffer from chronic pain, and the illness is one of the most expensive health care conditions to treat, costing up to $635 billion a year.
"Pain is becoming an enormous burden on the public. The US government recently outlined steps to reduce the future burden of pain through broad-ranging efforts, including enhanced research," says Linda Porter, pain and policy advisor at the National Institute of Neurological Disorders and Stroke (NINDS) and leader of the National Institutes of Health (NIH) Pain Consortium, which funded the study.
"This study is a good example of the kind of innovative research we hope will reduce chronic pain, which affects a huge portion of the population."