Surprising Source of Chronic Pain Discovered

Some types of ongoing, inexplicable pain like arthritis are caused by intact, healthy nerve fibers rather than those that have been damaged, a new study finds.

The discovery surprised researchers. It had not been made before partly because studies of chronic pain have tended to focus on the damaged nerves.

The new understanding, reported in the Jan. 25 issue of the journal Neuroscience, could help scientists develop new types of painkillers.

The evidence so far applies only to ongoing pain associated with nerve injury and inflammation, although it may turn out to be more widely applicable, said Sally Lawson, a professor of physiology at the University of Bristol in the UK.

What a pain

Information about pain is transmitted from its source by two types of nerve fibers, Lawson explained. Larger fibers send electrical signals more rapidly and are thought to communicate sharp, pricking pain.

Fine fibers communicate ongoing, burning pain that can prove depressing over time because it seems to have no identifiable source and is often hard to suppress with traditional painkillers.

Lawson and her colleagues Laiche Djouhri and Stella Koutsikou studied the ongoing pain and the firing in very fine fibers, in particular a type that serve as damage detectors. The faster they fire, the worse the ongoing pain becomes.

"The cause of this firing appears to be inflammation within the nerves or tissues, caused by dying or degeneration of the injured nerve fibers within the same nerve," Djouhri said.

Hope for some

More research is needed to figure out exactly which types of ongoing pain the discovery applies to, Lawson told LiveScience. Among the possibilities:

• Arthritis
• Chronic back pain
• Post-operative pain due to damage to nerves or tissues
• Trauma, especially injury to nerves, or inflammation
• Interstitial cystitis (a burning pain felt in the bladder)

"Further work is also needed to determine how the increased firing in the uninjured fine fibers could be prevented in order to alleviate the ongoing pain," Lawson said.

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