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.
Is the Mouse More Dangerous Than the Keyboard?
After following the study participants for one year and comparing types of computer work reported by the workers, researchers found no increase in symptoms of carpal tunnel syndrome associated with standard keyboard work. But they did find an increase of possible carpal tunnel symptoms among those who used a mouse for more then 20 hours per week.
Although this study confirms the low risk of carpal tunnel syndrome associated with moderate computer use, neurologist Richard Olney, MD, says several questions still remain.
"The biggest weakness of the study is that it didn't take one step further to see if those 'possible carpal tunnel syndrome cases' associated with mouse use were actually carpal tunnel syndrome," says Olney, who is a professor at the University of California in San Francisco.
Olney says the simplest way to confirm carpal tunnel syndrome is to perform a nerve conduction test that reveals whether the median nerve is responsible for the symptoms. But this study used only a clinical interview to confirm "possible carpal tunnel syndrome" cases. According to previous research, Olney says that only about a third of the cases that meet the clinical definition for carpal tunnel syndrome actually turn out to be carpal tunnel syndrome.
"It would also be useful to look at really high levels of computer usage [more than 30 hours per week] and use more objective measures to be certain if it's carpal tunnel syndrome or not," Olney tells WebMD.
Computer-Related Pain May Be Something Else
Researchers say their findings suggest that other factors may be causing the pain experienced by computer users. The study showed the onset of new symptoms was often linked to an accident, other medical disorders, and smoking.
"It is probable that tingling and numbness are common symptoms of either specific medical conditions other than carpal tunnel syndrome or are part of a large burden of medically unexplained symptoms that reflect the stresses and strains of everyday life," write the researchers.
Andersen says his advice to people who do a lot of computer work and suffer from hand and arm pain is don't jump to conclusions that it's carpal tunnel syndrome.
"Most likely, symptoms that are mild will disappear," Andersen tells WebMD. "If you have numbness or tingling exclusively in the first, second, or third fingers, the likelihood is much higher that it's carpal tunnel syndrome. But if it's in the whole hand, it's not likely that it's carpal tunnel syndrome."
Olney says that many people with carpal tunnel syndrome may not be able to precisely identify which fingers are affected by numbness and tingling. However, he says if the pain is nonspecific and occurs without those other symptoms, it's a good sign that the problem is not carpal tunnel syndrome.
Olney says other non-nerve related conditions, such as tendinitis, can cause carpal tunnel syndrome-like pain and numbness in the hands and arms. These conditions can be treated with anti-inflammatory drugs, occupational therapy, or some modification of work habits, such as making a more ergonomic workstation.