Award-winning actor Alan Alda has revealed he has Parkinson's disease.

The "M*A*S*H" star, 82, told CBS This Morning Tuesday that he was diagnosed with the disease three and a half years ago.

"The reason I want to talk about it in public is that I was diagnosed three and a half years ago and I've had a full life since then," he said. "I've acted, I've given talks, I help at the Alda Center for Communicating Science at Stony Brook, I started this new podcast."

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Alda said he decided to come forward with his diagnosis after seeing his thumb twitch in recent TV interviews.

"I thought, 'It's probably only a matter of time before somebody does a story about this from a sad turn point of view,' but that's not where I am."

Parkinson's is a nervous system disorder that affects movement and sometimes causes tremors. Other celebrities with Parkinson's include actor Michael J. Fox, who was diagnosed at age 29, and singer Neil Diamond, who shared his diagnosis earlier this year.

The actor said he was proactive in getting his diagnosis, asking for scans after he started "acting out" his dreams, which he read was a very early sign of the disease.

@CBSThisMorning tweet: "I asked for a scan because I thought I may have it... I didn't have any symptoms," Actor @AlanAlda says after revealing he has Parkinson's disease

"I was having a dream that someone was attacking me and I threw a sack of potatoes at them, but what I was really doing was throwing a pillow at my wife," he explained. "I didn't have any (other) symptoms, the doctor said, 'Why do you want a scan? You don't have any symptoms,' and I said, 'I want to know if there's any I can do, I want to do it before things start to show up.' "

Alda also shared a message of hope to those diagnosed with the disease.

"This is not to short-change people who are suffering with really severe symptoms," he said. "But in the very beginning, to be immobilized by fear and think the worst thing has happened to you, it hasn't happened to you, you still have things you can do."