NEW YORK - Every year, just more than four out of every thousand Swedish women are diagnosed with carpal tunnel syndrome, far fewer than those in the United States, according to a Swedish study.

For men, the number of new cases hovered just under two per 1,000 per year, according to the study led by Isam Atroshi at Hassleholm Hospital in Sweden and published in the Archives of Internal Medicine.

Carpal tunnel syndrome is a painful condition caused by a pinched nerve in the wrist. Though it sometimes goes away by itself, it may require treatment, with surgery possible to relieve pressure on the pinched nerve if wrist splints or corticosteroid hormone injections fail.

"A few studies have estimated the incidence of carpal tunnel syndrome (CTS), showing large differences between countries," wrote Atroshi.

"We estimate the incidence of physician-diagnosed CTS and surgery in the general population in southern Sweden and compare it with corresponding incidence in a US general population."

Previous studies have produced similar results.

One, which Russell Gelfman of the Mayo Clinic took part in, found that about twice as many people in Olmsted County, Minnesota, were diagnosed with carpal tunnel, compared to the rates seen in Sweden.

"This study adds to our observations that there are differences in the incidence of medically-attended carpal tunnel syndrome and surgical treatment between countries," he wrote in an email to Reuters Health. He was not involved in the recent study.

What accounts for the differences is still unclear, but both medical and social factors could be at play, Atroshi wrote.

For instance, it could be related to obesity or to different types of work, he added.

Carpal tunnel is often the result of repetitive motions that cause the ligaments in the wrist to become inflamed and pinch a nerve.

Gelfman said that as many as 15 percent of the population may have symptoms, but only about five percent or fewer are diagnosed with carpal tunnel syndrome.