Study Finds Nerve Damage Can Affect Opposite Side Of Body

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Study Finds Nerve Damage Can Affect Opposite Side Of Body

BOSTON - April 2, 2004 - Researchers from Massachusetts General Hospital

(MGH) have found physical evidence of a previously unknown communication

between nerves on opposite sides of the body. In the May 2004 issue of

ls of Neurology, the scientists describe how cutting a major nerve in

one paw of a group of rats resulted in a significant decrease in skin nerve

endings in the corresponding area of the opposite limb. The study, released

on the journal's website, may have major implications for the care of

patients with nerve damage and also calls into question the common practice

of using tissues on the opposite side of the body as controls in scientific

experiments.

" Patients with pain syndromes related to nerve damage sometimes report

symptoms on the side opposite their injury as well, but those reports are

usually discounted because there has been no biological framework for the

phenomenon, " says Anne Louise Oaklander, MD, PhD, director of the MGH Nerve

Injury Unit, the report's principal author. " Our evidence means that these

reports can no longer be ignored and gives us a new direction for research. "

It has been known for more than 100 years that, when a nerve is cut, skin

nerve endings in the area supplied by that nerve quickly disappear. This is

because nerve cell bodies are actually located near the spinal cord, and

nerve fibers called axons extend into the limbs. When axons are severed,

downstream nerve endings are cut off from the cell body and die.

Reports of opposite-side sensory effects of injury date back to the American

Civil War. However, no connections are known to exist between nerve cells

supplying corresponding areas on the left and right sides. In previous

research Oaklander and her colleagues examined nerve endings in patients

with post-herpetic neuralgia - persistent pain in an area of skin previously

affected by shingles, also called herpes zoster. Along with an almost total

loss of nerve endings at the site of the shingles outbreak, they also found

that almost half the nerve endings on the opposite side skin had been lost,

even though patients did not report pain on that side. But since shingles is

caused by the varicella zoster virus, which also causes chicken pox, there

was a possibility that the damage had been caused by viral spread through

the spinal cord.

In the current study, Oaklander and her co-author Brown describe

their experiment in three groups of rats - an experimental group in which

the tibial branch of the sciatic nerve was cut in one hind paw and two

control groups, one which had sham surgery and the other had no procedures.

Within one week of injury, rats in the experimental group lost almost all

skin nerve endings in the part of the paw supplied by the tibial nerve.

Surprisingly, they also lost 54 percent of nerve endings in the

corresponding area in the opposite paw. No changes were seen in either

control group. The researchers also examined the opposite-limb-area supplied

by the uncut nearby sural branch of the sciatic nerve and found no change in

nerve endings.

" This loss of nerve fibers in the contralateral limb is so precise - being

confined to areas innervated by the matching nerve - that the communication

is likely to involve nerve cells or the supporting glial cells, " says

Oaklander, an assistant professor of Anesthesia and Neurology at Harvard

Medical School. " We need to look into what regulates this communication and

how it may be altered to help treat nerve injury and pain patients. "

This study was supported by grants from the National Institutes of Health

and a Beeson Award from the American Federation for Aging Research.

Massachusetts General Hospital, established in 1811, is the original and

largest teaching hospital of Harvard Medical School. The MGH conducts the

largest hospital-based research program in the United States, with an annual

research budget of more than $400 million and major research centers in

AIDS, cardiovascular research, cancer, cutaneous biology, medical imaging,

neurodegenerative disorders, transplantation biology and photomedicine. In

1994, MGH and Brigham and Women's Hospital joined to form Partners

HealthCare System, an integrated health care delivery system comprising the

two academic medical centers, specialty and community hospitals, a network

of physician groups, and nonacute and home health services.

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