Washington: U.S. health officials on Friday warned kidney disease patients about a new disease that can cause hardened skin and muscle weakness in those who resonance have certain magnetic scans like an MRI.

The new condition, called nephrogenic systemic fibrosis ornephrogenic fibrosing dermopathy, has been found in more severe kidney disease patients who had a scan using contrasting agents containing the metal gadolinium, the Food and Drug Administration said.

So far, 90 patients in the United States and 215 worldwide have reported the new condition, the FDA said in a statement,and the metal was found in patients' skin.

Agency officials said they did not know what caused the disease but would work to gather more information. About 20 million Americans have been diagnosed with chronic kidney disease, according to the National Kidney Foundation.

Commonly caused by diabetes, high blood pressure or heredity, kidney disease impairs a patient's ability to filter waste products from the blood.

Magnetic resonance scans are used to help detect damage to the kidneys, and contrast agents can help show cysts and other problems more clearly. The fibrosis can cause scarring to body organs, yellow spots on the eyes and joint stiffness, in addition to skin troubles that include burning, itching and swelling.

Patients with moderate to end-stage kidney disease who think they may have the condition should contact their doctor,the agency added. Those who need a scan should use alternatives whenever possible, it said.

The FDA said contrast agents containing the metal include Tyco unit Mallinckrodt's Optimark, General Electric unit GEHealthcare's Omniscan, Schering AG unit Berlex's Magnevist, and privately-held Bracco Diagnostic's Multi-Hance and ProHance.