Nerve Damage May Spur 'Sick Worker Syndrome'

Repetitive strain caused mice to abandon former tasks, researchers say

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FRIDAY, Nov. 11, 2005 (HealthDay News) -- "Sick worker" syndrome -- often mistaken for poor performance and characterized by fatigue, malaise and depression -- can be caused by early nerve damage linked to repetitive strain injuries, researchers report.

In research with rats, the scientists found that nerve injuries caused by low-force, highly repetitive movement can be caused by cytokines, proteins that help trigger inflammation. Cytokines, which are also known to cause symptoms of malaise, appear in injured nerves as early as three weeks after the initial signs of cell stress. This is much earlier than previously believed, according to the research team.

"At three weeks, even before the rats experienced pain from their wrist injuries, we watched them self-regulate their work behavior. With inflammatory proteins in the bloodstream, they began to slack off from completing their tasks," study co-author Ann Barr, of Temple University's College of Health Professions, said in a prepared statement.

As the rats' nerve injuries progressed, even higher levels of cytokines were made at the site of the nerve injury.

The study also found that the cytokines had an effect on the rats' psychosocial responses, resulting in a rat version of "sick worker" syndrome. It's believed this was caused by cytokines that traveled through the bloodstream to the rats' brains.

When cytokine production reached its peak at five to eight weeks, some of the rats curled up and went to sleep in between their tasks.

"Cytokines are self-protective. This undefined feeling of malaise may be telling the body to take some time off the heal, before things get worse," co-author Mary Barbe said in a prepared statement.

The researchers said their findings, published in the October issue of the Journal of Neuroimmunology, may help in the development of early intervention techniques to prevent permanent damage caused by repetitive strain injuries.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about repetitive motion injuries.

SOURCE: Temple University, news release, Oct. 24, 2005

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