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Brain may hold key to chronic low back pain.

CHICAGO -- Spine specialists have traditionally focused on specific degenerative pathology in the spine as the main determinant of back pain, but science now suggests that the central nervous system ultimately modulates chronic low back pain.

Acceptance of the new evidence will require a fundamental shift in thinking by spine surgeons and could lessen the role of surgery and increase the role of exercise in the management of low back pain at a time when critics are assailing the overuse of spinal fusion surgery in the United States.

"We've been looking for decades for where the smoking gun is as to why these people are having back pain, and so far we haven't found it," James Rainville, M.D., said at the annual meeting of the North American Spine Society. "There is now some information coming out to show what is going on, and [pain processing] may not be where we thought it was. It may be happening in the central nervous system."

Less well known than the spinal cord's role in pain production is the part the spinal cord plays in pain augmentation, said Dr. Rainville, chief of rehabilitation at New England Baptist Hospital, Boston.

Wide dynamic range neurons have been identified in the spine as responsible for "windup," or the accentuation of painful stimuli.

A recent study found evidence of central nervous system augmentation of pain processing in patients with chronic low back pain (Arthritis Rheum. 2004;50:613-23). Experimental pain testing at the thumb revealed hyperalgesia in patients with idiopathic chronic low back pain as well as in patients with fibromyalgia, compared with controls.

Moreover, functional magnetic resonance imaging detected five common regions of neuronal activation in pain-related cortical areas in the low back pain and fibromyalgia groups. The areas are responsible for the transmission of neurologic information into the conscious experience of pain and included the contralateral primary and secondary somatosensory cortices, inferior parietal lobule, cerebellum, and ipsilateral secondary somatosensory cortex. The same stimulus resulted in only a single activation in controls in the contralateral secondary somatosensory cortex.

Finally, these studies' findings are strengthened by research that suggests that thoughts can change brain activity induced by peripheral stimulation (J. Neurosci. 2004;24:7199-203).

"Could our thoughts, ideas, and feelings that we have all be acting through central mechanisms to change our central sensitization to pain? If that's the case, then we're in trouble if we're trying to treat it in the periphery always," observed Dr. Rainville, of Harvard Medical School.

This has important implications for understanding the successes and failures of spinal surgery. Spine surgeons came under fire recently in an editorial (N. Engl. J. Med. 2004;350:722-6) that charged fusion surgery was being overused in the United States. NASS fired back with an editorial of its own (Spine J. 2004;4[suppl. 5]:S129-38) and a high-profile panel discussion at the annual meeting.

Still, several studies presented at the same meeting validated a different approach. The rehabilitation model suggests that pain can be stopped by desensitizing the pain-producing tissue and improving central processing.

Exercise can improve muscle strength and flexibility, reduce disability, and even reduce pain intensity by 10%-50%. Exercise also can alter a patient's pain attitudes and beliefs.

A recent study by Dr. Rainville and colleagues showed that exercise reduced both the pain anticipated before and induced with exercise.

Significant improvements were observed for global back pain, leg pain, disability, and performance on each physical testing in 70 patients with chronic low back pain who completed an intensive 2-hour exercise program delivered up to three times per week for 6 weeks.

Performances on all physical testing correlated with anticipated and induced pain for all tests at baseline, but only for measures of flexibility at discharge. The correlation between disability and pain attitudes and beliefs was extremely high, at 0.79.

"Something about the pain process has been changed," Dr. Rainville said. "What, I don't know. Where, I don't know. But it's a fascinating observation. In addition, people improved their strength. They have less pain with lifting a lot more. Something has been learned differently within the central nervous system, because we didn't change their anatomy in any positive way."

Finally, exercise may help wean patients with chronic low back pain from narcotics. After 6 weeks of exercise therapy, one-half of patients in the study who regularly used narcotics were able to stop taking them.

BY PATRICE WENDLING

Chicago Bureau
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Title Annotation:Pain Medicine
Author:Wendling, Patrice
Publication:Clinical Psychiatry News
Geographic Code:1USA
Date:Feb 1, 2005
Words:736
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