Kutcher discusses vasculitis on "Running Wild with Bear Grylls: The Challenge."

Ashton Kutcher is "fortunate to be alive" after a rare condition damaged his vision, hearing, and walking.

Kutcher discusses his struggle with vasculitis on Monday's episode of "Running Wild with Bear Grylls: The Challenge"

"Access Hollywood" released video of Kutcher explaining his illness.

In the episode, Grylls questions Kutcher about his source of strength.

Kutcher says: "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 informs Grylls that it took him approximately one year to regain these skills.

Vasculitis is a group of uncommon conditions characterized by inflammation of the blood vessels.

According to the Mayo Clinic, general symptoms of vasculitis can include fever, weight loss, and pains.

Additionally, the condition can produce more severe symptoms, such as deafness, blindness, ulcers, skin sores, and shortness of breath.