Actor Ashton Kutcher says he suffered life-changing health issues that limited his ability to see, hear, and walk. He revealed his devastating diagnosis in a recent episode of National Geographic's "Running Wild with Bear Grylls: The Challenge".

"Two years ago, I had this weird, super-rare form of vasculitis that knocked out my vision. It knocked out my hearing. It knocked out all my equilibrium," the 44-year-old "That 70's Show" actor said, according to TODAY.

Vasculitis involves inflammation of the blood vessels, says the Mayo Clinic. The inflammation can cause the walls of the blood vessels to thicken, which narrows the width of the passageway through the vessel. If blood flow becomes restricted, it can result in organ and tissue damage.

There are many types of vasculitis and most of them are rare. The disorder can affect one organ or multiple sites and can be short-term or long-lasting. It can attack the digestive system, the ears, eyes, hands, or feet and even the lungs and skin, says the Mayo Clinic.

Loss of hearing and sight are signs of vasculitis, as Kutcher experienced.

"You don't really appreciate it until it's gone," he said, referring to his loss of sight. "Until you go 'I don't know if I'm ever going to see again, I don't know if I'm every going to hear again, I don't know if I'm ever going to walk again'."

The exact cause of vasculitis is not known, the Mayo Clinic noted, according to TODAY. Some cases are caused by genetics while others are triggered by the immune system and immune disorders, like rheumatoid arthritis and lupus.

Age, ethnicity, family history, and lifestyle factors such as smoking and illegal drug use can increase the risk for vasculitis, according to the National Institutes of Health.

Certain medications for high blood pressure, thyroid disease, and infections can also contribute. According to the American College of Rheumatology, early detection and treatment of vasculitis can prevent permanent damage.

Detection requires blood tests and biopsies of the affected tissue. Mild cases respond to over-the-counter medications, but severe cases need powerful prescription medications.

Because vasculitic diseases are inflammatory health issues, they are often treated with glucocorticoids or immunosuppressive drugs.