Chronic Pain Is Hard On The Brain

Chronic pain prematurely ages the brain. That was the most significant - and disturbing - finding of a group of researchers from Northwestern University. Scientists have known for some time that chronic pain alters neurons in the spine, but Dr. Apkarian, a neuroscience researcher, and his colleagues wanted to know if and how chronic pain effected the structure of the brain.

In order to study this, Dr. Apkarian and his team used MRI's to measure the volume and density of the brains of 26 people with chronic back pain (CBP) and compared them to the brains of 26 healthy volunteers. They published their results in the November 17, 2004 issue of the Journal of Neuroscience.

Each of the 26 members of the pain group had experienced unrelenting pain for more than a year in their lower back. In some, the pain radiated down into the legs, in others it didn't. In addition to the brain MRI's the CBP subjects reported their pain intensity and how long they had been in pain. To aid in the analysis, members of the pain group were also classified as having neuropathic pain - due to nerve damage - or non-neuropathic pain. The 26 volunteers that composed the control group were recruited to match the age and gender makeup of the CBP group as closely as possible.

The researchers used two different techniques to measure the volume of the neocortical gray matter (the part of the brain responsible for most higher order functions) from the MRI's. They found that overall, the subjects in the pain group had 5%-11% less gray matter volume than the control subjects, a statistically significant finding. People normally lose about 0.5% of their gray matter each year as they age, so this result translates to the pain patients experiencing 10-20 years of aging compared to the control group.

In looking at neuropathic versus non-neuropathic pain, the team found that in the neuropathic pain group, the volume loss was related to pain duration. In fact, in the neuropathic group, each year of pain equated to a 0.2% loss in gray matter (1.3cm3). In the non-neuropathic group, pain duration was not related to volume loss.

The neuropathic pain group also fared worse when the team measured the density of the gray matter in specific regions of the brain. In the prefrontal cortex - responsible for high level functions - they found that people in neuropathic pain had gray matter that was 27% less dense than the control group, and people with non-neuropathic pain had gray matter that was 14% less dense. They also found that the thalamus - a region of the brain which relays pain and other sensations - was significantly less dense in the pain group as compared to the control group.

Although this study can not prove it conclusively, the authors believe the results mean that the chronic back pain is causing brain tissue to atrophy in certain areas. If proven to be true, this would mean that chronic pain not only alters the neurons of the spine, but has a structural effect all the way to the brain as well. While it is a significant finding, it is also important to keep in mind that this study looked at chronic back pain specifically and the results may be different for other types of chronic pain.

Still, with millions of people in the US alone suffering from chronic pain, and with neuropathic pain an all too common problem for CM/SM patients, this area of research is definitely worth paying attention to..

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