ATLANTA -- U.S. Health experts said on Thursday they were mystified by the emergence of a new skin condition that has left debilitating scar tissue on a small group of kidney patients in the United States and Europe.

The centers for disease control and prevention said 49 people with poorly functioning kidneys in Switzerland, England and several U.S. states had developed itchy, wood-hard patches of skin on their hands, forearms and other parts since 1997.

"Their skin contracts so much that they actually lose some of their extension abilities," said Dr. Michelle Goveia, a CDC epidemiologist who is investigating the condition in conjunction with the California Department of Health services.

"People have lost their ability to drive and have been put in wheelchairs because they can't walk properly," Reuters quoted Goveia, who noted that some of those diagnosed so far had shown improvement over time, as saying.

Patients have ranged from 8 to 72 years old.

The Atlanta-based CDC said there was no known cause for the condition, which resembles but is different in several clinical and pathological aspects from the rare but potentially fatal skin disease scleromyxedema.

The agency said a case-control study last year involving eight people who developed the new condition after undergoing kidney transplants at a California hospital showed that the sufferers were more likely to have poorer renal functions after kidney transplants.

They were also more likely to require dialysis and drug therapy associated with severe kidney disease.

The CDC conceded the case-control study was small and said it should be expanded to include other reported cases, including those among people who had not had kidney transplants.

Some people with skin conditions such as scleromyxedema have reported finding relief from Vitamin E therapy as well as photopheresis, in which patients' white blood cells are exposed to ultraviolet light.