June 10, 2003 -- Contrary to popular belief, hours of typing away at a computer isn't a likely cause of carpal tunnel syndrome.

A new study suggests that typing on a computer keyboard for more than 20-25 hours per week doesn't increase the risk of tingling, numbness, and pain in the hands and arms associated with carpal tunnel syndrome.

Although the common perception has been that computer use may be linked to carpal tunnel syndrome, researchers say this study provides convincing evidence that working at a computer isn't an occupational hazard for developing the condition.

"The occurrence of carpal tunnel syndrome is lower than what many people expect among heavy computer users," says researcher Johan Andersen, MD, PhD, of the department of occupational medicine at Herning Hospital in Herning, Denmark. "But it looks as if working with your mouse could be a little worse than working on a keyboard."

Carpal tunnel syndrome is a disorder caused by repetitive use, physical injury, or other conditions that cause the tissues that surround the median nerve, which stretches from the forearm to the hand, to become swollen and inflamed. This leads to symptoms such as pain, numbness, and tingling in the fingers, wrist, and hand.

Researchers say it's clear that industrial jobs that require repetitive, forceful work such as operating a jackhammer can cause carpal tunnel syndrome, but the role of computer use, which involves repetitive but nonforceful movements, is not clear.

The study, which appears in the June 11 issue of The Journal of the American Medical Association, involved more than 5,600 technical assistants from more than 3,500 workplaces in Denmark where computer use was common.

About 11% of the workers reported tingling or numbness in the right hand at the start of the study, and the median nerve (the nerve involved in carpal tunnel syndrome) was confirmed as the culprit in about 5%. Of those, only about 1.4% experienced their symptoms at night, which is a classic sign of carpal tunnel syndrome.

Researchers say previous studies have shown similar rates of carpal tunnel syndrome in the general population.