Alan Alda said he has had “a full life” since he was diagnosed. (Richard Drew/AP)

Actor Alan Alda, known for his roles on “M.A.S.H.,” “The West Wing” and “The Aviator,” announced on Tuesday that he has Parkinson’s disease.

Speaking on “CBS This Morning,” Alda said he has had “a full life” since he received the diagnosis 3½ years ago.

“I’ve acted. I’ve given talks. I help at the Alda Center for Communicating Science at Stony Brook. I started this new podcast. And I noticed that I had been on television a lot in the last couple of weeks talking about the new podcast, and I could see my thumb twitch in some shots,” said Alda, 82. “I thought, it’s probably only a matter of time before somebody does a story about this from a sad point of view, but that’s not where I am.”

Parkinson’s disease is a nervous system disorder affecting movement, though symptoms are mild in the early stages. Although there is no cure, there are medications and other options that can help patients with symptoms.

There is no specific test for Parkinson’s, which is diagnosed by doctors taking into account one’s medical history, conducting a neurological and medical exam, and reviewing one’s symptoms. There is a scan that can help support a doctor’s diagnosis.

Alda explained that he had read an article about a study showing that acting out one’s dreams could be a very early indicator of Parkinson’s, when no other symptoms show. So he asked doctors for a scan “because I thought I might have it.”

“And by acting out your dreams, I mean I was having a dream that someone was attacking me and I threw a sack of potatoes at them,” Alda said. “But what I was really doing was throwing a pillow at my wife.”

He added that he wanted to know early on so that “if there’s anything I can do,  I want to do it before things start to show up.” Months later, he noticed things such as “a little twitch in my thumb.”

Alda said there are “people who are suffering with really severe symptoms. Symptoms can get very bad, and their families can suffer.” But for him, at this stage, he doesn’t want to be immobilized by fear.

The actor — who takes boxing lessons and plays tennis three times a week — says he’s been in movies since his diagnosis. “It hasn’t stopped my life at all. I’ve had a richer life than I’ve had up until now.”

“I think my saying something publicly about this today is going to make one thing a little easier,” he said Tuesday. “I’m not going to worry while I’m trying to say something else; I’m not going to be thinking is my thumb on a life of its own. That’s just one of the realities of my life.”

During Alda’s long career, he has played a range of roles, from Jack Donaghy’s father on “30 Rock” to host of the PBS series “Scientific American Frontiers” for 13 seasons. He has also won six Emmys and six Golden Globes.

There is a center at Stony Brook University named after Alda focused on helping medical professionals and scientists communicate with patients and the public. “It would be kind of ironic if I get quiet about this,” Alda said.

“Because I’m sort of well known, it might be helpful to people to hear the message that there are things you can do, if you learn about things and not follow quackery but found out what real science is coming up with that helps.”

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