Ashton Kutcher has said he is “lucky to be alive” after a he was diagnosed with an autoimmune disorder that he says robbed him of sight, hearing and equilibrium.

The actor revealed his diagnosis with vasculitis – an autoimmune disease that inflames the blood vessels – during an episode of Running Wild With Bear Grylls: The Challenge.

In a clip from the program released ahead of its broadcast, the star and venture capitalist told host Grylls that the affliction had come on two years ago, and it had taken a year to recover.

“You don’t really appreciate it until it’s gone, until you go, ‘I don’t know if I’m ever gonna be able to see again,’” Kutcher said. “I don’t know if I’m gonna be able to hear again, I don’t know if I’m going to be able to walk again.’”

Kutcher, known for his roles in That ’70s Show and The Butterfly Effect, added that he was “lucky to be alive” after what had been “a terrifying journey”, but one that made him strong and resilient.

Common symptoms of vasculitis, which causes blood vessels to swell and narrow, include fever, headache and fatigue. It can also cause ringing in the ears, numbness in the extremities and bleeding in the lungs. At its most extreme, it can cause blindness or aneurysms.

Kutcher did not reveal which type of the ailment he’d suffered from.

Questions about the autoimmune disease, which can occur in the young and old, grew more acute at the height of the Covid-19 pandemic when American and British health agencies warned of a possible link between Covid-19 and Kawasaki disease, a type of vasculitis found in children.

The US Centers for Disease Control and Prevention cautioned against drawing connections between Kawasaki disease and Covid-19.

During the clip, which was filmed in what appeared to be a dense forest, Grylls chimed in empathically.

“What do they say in survival?” Grylls remarked. “Storms make you stronger, and I think he is living proof of that.”