The Centers for Disease Control is expanding its investigation of an unusual skin condition first discovered in eight persons who had kidney transplants between 1997 and 2000 at the University of California, San Francisco.

The condition creates "large areas of hardened skin" with small bumps on the chest, hands and feet that becomes so tight that it results in "severe contractions and limited mobility," according to the CDC.

"Their skin feels like wood," said Dr. Michelle Goveia, a CDC epidemiologist. "You knock on it, and it sounds like you're knocking on wood. Their skin's so tight and taut and thick that they can't extend their extremities anymore."

The CDC said that in the past year, it has identified an additional 41 cases of the diseasse in the United States and Europe -- all among people with underlying kidney disease and about half of whom have had kidney transplants.

The CDC said patients with the skin disease were more likely than controls to "have poor renal function post-transplantation, which included requiring hemodialysis and receiving medications associated with severe disease.

"Some of the patients have improved, but there is no known treatment," the CDC said.

While doctors said the fibrotic skin lesions found on patients resembled those of scleromyxedema, tests appeared to have eliminated that possibility.

The CDC appealed to doctors in its regular Thursday bulletin to report information about additional patients with this condition to expand the study of this disease.