What is vasculitis? Ashton Kutcher says he battled rare autoimmune disease that left him unable to walk, hear and see

Ashton Kutcher revealed he battled a rare autoimmune disease that left him unable to walk, hear and see, saying he felt "lucky to be alive" after he recovered. 

Kutcher explained that he suffered from vasculitis in the National Geographic show, "Running the Wild with Bear Grylls: The Challenge." A preview clip of his revelation was published by Access Hollywood ahead of Monday's episode. 

"Like two years ago, I had this weird, super rare form of vasculitis, that like knocked out my vision, it knocked out my hearing, it knocked out like all my equilibrium," Kutcher told Grylls.