Sept. 18--It's infuriating to chronic pain sufferers to be told their pain in
"all in the head." But a new study offers strong evidence that even before a
person experiences an injury, the likelihood that the resulting pain will become
chronic can be predicted by examining the brain's "white matter" -- the bundles
of fatty fibers that carry electrical impulses between the brain's hemispheres
and among its dense network of cells and structures.
The new research, published Tuesday in the journal Pain, suggests that
variations in brain structure could help identify people who, once injured, are
more vulnerable to becoming chronic pain sufferers. But it will take further
research to identify whether and which treatments could discourage short-term
pain from settling in for a long stay.
The study was conducted by researchers at Northwestern University's Feinberg
School of Medicine, led by Ali R. Mansour and A. Vania Apkarian, both pioneers
in defining the link between pain and emotion.
Research has shown that there are clear differences that distinguish the brains
of those with chronic pain from those without such pain. Chronic pain sufferers
consistently show reduced volume in the brain's gray matter, the cortical
structures key to perception, movement, memory and reasoning. Researchers have
also shown that compared to healthy patients, the brains of chronic pain
sufferers are wired differently, in ways that suggest that physical sensations
and emotional responses are bound more tightly together.
But are those brain differences a response to chronic pain -- the brain's
response to the experience of months or years of physical misery? Or do those
differences predate chronic pain -- nudging what for another patient would be a
short-term experience of discomfort into a lifelong ordeal? The authors of the
current study, working under a federal government initiative aimed at
consolidating research on pain, devised a series of experiments designed to
clarify which came first.
They did so by recruiting 46 subjects who had experienced a first episode of
back pain that had already lasted four to 16 weeks, and performing regular brain
scans on those subjects for a year. Focusing largely on the bundles of axons
that carry nerve impulses across the brain, they found that within two months of
recruiting patients, discernible differences in the structure and integrity of
that "white matter" could be used to distinguish subjects whose pain persisted
from those whose pain was beginning to resolve.
By the 12-month mark, the structural differences in white matter allowed
researchers to distinguish -- without error -- subjects whose pain had
disappeared from those whose pain was persistent. Compared to subjects whose
pain resolved, subjects whose pain would become chronic also showed differences
in the density of connections that lashed their nucleus accumbens -- a central
structure in the brain rewards, motivation, pleasure and reinforcement learning
circuit -- together with their medial prefrontal cortex, a switchboard for
decision-making, emotional response and long-term memory.
The authors made further comparisons between the original 46 subjects and two
new groups: healthy recruits and people with a established history of chronic
pain. Those comparisons showed that, from the earliest scans, the brains of
subjects who would go on to become chronic pain sufferers had structural
abnormalities that made them look much more like the chronic pain veterans than
like healthy controls or the subjects with back pain that went away.
And throughout the study period, the white matter and brain connections of
subjects with back pain that went away looked much more like those of healthy
control subjects than they did like the brains of subjects whose pain became
The brain's white matter normally deteriorate with age, and the Northwestern
researchers made a shocking calculation to show the difference that separated
subjects with and without chronic pain: Compared to healthy controls or those
whose pain subsided, the white matter in the subjects whose pain went on to
become chronic "exhibits 30 to 50 years of additional aging."
If this research holds up, future patients may want to know what the stakes are
if they get hurt, and make their recreational and career choices accordingly.
So, too, might their prospective employers -- including the armed forces, the
National Football League, or a trucking company tired of paying disability to
drivers retiring with chronic back pain.
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