WASHINGTON, Feb 22 (Reuters Health) -- Chronic pain should be viewed as a
disease, not just a symptom, according to experts who spoke at the recent annual
meeting of the American Association for the Advancement of Science.
Acute pain from an injury, such as a broken bone, helps to warn the
patient to rest, and is usually treated easily. However, chronic pain caused by
nerve injury or inflammation should be viewed differently, said Dr. Alan Basbaum
from the University of California, San Francisco.
"Persistent pain is in fact a disease," he said. "Many of the changes that
occur actually occur at the level of the spinal cord, and it occurs in some
respects by the establishment of memories of pain, memories of the injury, long
lasting memories." In other words, in addition to pain at the site of the
problem, "the pain is in the brain," he said.
"One of the big breakthroughs in my mind has been the recognition that
many elements in the pain transmission system uniquely express molecules that
are not found anywhere else in the brain," he continued. These include molecules
such as the receptor for capsaicin, the chemical that gives hot peppers their
spicy taste. These receptors provide new therapeutic targets for drug
development, he concluded.
Also at the meeting, Dr. Jeffrey Mogil of the University of Illinois,
Urbana-Champaign, discussed his studies examining why pain response varies
widely between individuals. In studies of mice, he has found that about 50% of
the variability is due to genetic factors.
"The fact that there is such variability in humans in pain responses, and
the fact that a goodly percentage of that variability is genetic, hopefully
should lead to a destigmitization of pain-sensitive individuals," he said. In
the future, knowing the genes involved in pain sensitivity could also allow
individualized therapy for pain and the development of novel pain therapies.
Dr. Catherine Bushnell of McGill University in Montreal, Canada, told the
audience of her studies in humans looking at the sensory and emotional
components of the pain experience in the cerebral cortex. Using brain imaging,
she also found "huge" individual variation in how people experience the same
type of pain, represented as different patterns of activity in the brain.
"No matter how the pain is produced, ultimately there is a common circuit
that tells the person that this is pain," she said. She has also found that
people with injury to the central nervous system that causes chronic pain have a
reorganization of the sensory part of the cortex that appears to be maintained
by the pain.
Brain imaging has also shown that a person's emotional state affects pain
perception. "Psychological manipulation such as distraction actually
activates... modulatory circuits in the brain that leads to reduction of pain
transmission in the same way as if you had given the person morphine or some
other analgesic," she said.
