The first symptom of carpal tunnel syndrome, often felt at night or on waking, is numbness or tingling in the thumb and middle fingers. Often shafts of burning pain shoot from the palm to the shoulder.

The disorder seems to be characteristic of the age. Although the disease is no doubt ancient, only in the past few years has it come to be widely recognized and partly understood.The cause can be diabetes, pregnancy, thyroid disorders, inflammatory arthritis, an accident to the hand, even alcohol use.

But as often as not the cause is the sufferer's job. Physicians in one recent survey by the California Occupational Health Program believed half of the cases they saw were occupational. The culprit: using the hands too often, too forcefully and in the wrong positions.

Among the workers most susceptible are grocery clerks, garment and other assembly-line workers, carpenters, meat and poultry workers and anyone who works with a computer keyboard.

"No reliable data exist," the Centers for Disease Control reports, "on the frequency of work-related CTS in the general working population."

The carpal tunnel is a gap in the wrist, two-thirds surrounded by bone and one-third by the bandlike carpal ligament at the base of the palm. The hand's median, or main, nerve runs from the arm through the tunnel, cushioned by fluid.

When trauma or overuse inflames the ligament, it compresses the fluid and the nerve, causing pain. One source of inflammation is repetitive use of wrist and hand muscles when the hands are flexed.

Many keyboard users, for example, are forced by the height of their chairs and desks to type for hours with palms bent back from the wrist. People who trim meat off animal carcasses, similarly, must execute swift movements all day, their hands skewed at uncomfortable angles.

Relief for carpal tunnel syndrome can be found through treatment, which usually begins with medication and forearm "cockup" splints that force the hand to stay in a neutral, unflexed position.

If those fail, surgery can relieve pressure on the nerve. But several neurologists writing in a recent issue of the journal Patient Care suggest it's an easy operation to botch. "Total functional loss of a hand may result from poorly done hand surgery for carpal tunnel syndrome," the physicians write.

Prevention is the better bet. It's vital to change working conditions so that repetitive motion is reduced and made more ergonomically sound. Keyboards should be placed, for example, low enough to allow typing without a flexed hand.

The same is true for any manual task. Some industries - prodded by their newly aware employees - are considering equipment and policy changes that allow for healthier hand positions while working.