Atlanta ? Federal health officials are warning doctors that certain types of metallic dye injected for MRI scans have been linked to a rare and dangerous skin disease in kidney patients.

More than two dozen dialysis patients in St. Louis over a four-year period contracted the unusual skin ailment, which causes burning and itching that can lead to discoloration and stiffening of the skin.

The U.S. Centers for Disease Control and Prevention investigated a number of the cases last year and found the illnesses were tied to a contrasting agent – basically a metallic dye – used for magnetic resonance imaging tests. The disease occurred in patients with advanced kidney disease who had undergone an MRI or a similar test.