Chronic, Phantom Pain Is from Affected Nerve Not Brain

By some accounts, chronic pain affects nearly 100 million Americans from such varied causes as arthritis, sciatica, cancer, diabetes. Most forms of pain result from identifiable causes which serve the "good" purpose in warning of a real physical problem that needs attention, or rest.

Another kind of chronic pain may start with a specific injury, surgery or disease event, but may linger for weeks or even years beyond any useful protective function. Such events range from shingles to open-heart surgery where up to half the patients suffer long-term pain, breast removal (sometimes even lumpectomies), or - in the most drastic cases, spinal injury or amputation.

Such "neuropathic pain" is particularly vexing and difficult to treat because there's no agreed location or physiological mechanism to target for therapy. New research from the University of Alberta, Canada appearing in the Journal of Neurophysiology reported that the place to look is between the nerves that are producing the pain and the spine, rather than from the spine to the brain, according to the senior author, Peter A. Smith.

The paper, "Sciatic chronic constriction injury produces cell-type specific changes in the electrophysiological properties of rat substantia gelatinosa neurons," is in the online Journal of Neurophysiology, published by The American Physiological Society. Research was by Sridhar Balasubramanyan, Patrick L. Stemkowski, Martin J. Stebbing and Peter A. Smith, University of Alberta, Canada; Stebbing is also at RMIT University, Bundoora, Australia.

Importance of identifying peripheral nerves as key target

Marshall Devor, a professor at the Institute of Life Sciences, and at the Center for Research on Pain, Hebrew University, Jerusalem, said "the results reported in this paper are quite optimistic in terms of the prospects for finding future methods of treatment. First," he said, "because if the problem is in the spine or the brain, it's hard to treat. But if the impact is in the nerve, we have a better idea where to look and it's also easier to target therapy there."

Devor added that the Alberta team "didn't prove that the central nervous system isn't involved, but they have shown that the peripheral nerve probably is highly involved." Devor wrote an editorial in the Journal accompanying the Balasubramanyan et al. paper.

Paradoxes abound: role of inflammation, contrary reactions; Iraq casualties

"The subject gets complicated quickly and is full of paradoxes," Smith said: "For instance, in chronic pain there's often an emotional element. If a patient has post-traumatic stress syndrome, that could make the pain worse because there are overlapping disorders."

The war in Iraq has highlighted the issue of chronic neuropathic pain in amputations (called "phantom limb pain") because the rate of amputations is so high compared to previous wars.