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. 

Kutcher said it took him a year to build himself back up. 

"You don't really appreciate it, until it's gone," Kutcher said, "Until you go, 'I don't know if I'm ever going to be able to see again, I don't know if I'm ever going to be able to hear again, I don't know if I'm ever going to be able to walk again'."

"Lucky to be alive," he added.

It's unclear exactly when the episode was filmed, but Kutcher further elaborated on Twitter that he had the "rare vasculitis episode" three years ago, resulting in impairments to his hearing, vision and balance. However, he said he was past the medical issue. 

"I fully recovered. All good. Moving on. See you at the 2022 NY Marathon w/Thorn," he wrote. 

What is vasculitis?

The Mayo Clinic describes vasculitis as "inflammation of the blood vessels," which can cause walls of the cells to thicken and reduce the width of the passageway through the vessel. 

"If blood flow is restricted, it can result in organ and tissue damage," the Mayo Clinic says on its website.

Vasculitis can impact one or multiple organs — and the condition can be short or long term, according to the Mayo Clinic. Symptoms of the disease include fever, fatigue, weight loss, general pains and aches, digestive system issues, dizziness, ringing in the ears, abrupt hearing loss, temporary or permanent blindness and shortness of breath. 

Editor's note: This story has been updated to reflect that vasculitis is an inflammation of blood vessels, not blood cells.