It began with shaking in his hands. Go get tested, the daughter of John L. O’Brien Jr., the long-serving Southern Essex District register of deeds, urged.

The diagnosis was devastating: Lewy body dementia, with Parkinsonian symptoms.

The symptoms can unfurl slowly, but O’Brien made a quick decision: He would not hide his disease. On Monday, O’Brien announced his condition in a written statement, declaring, “If I worked in a private industry I would want my boss to know.’’

In this case, O’Brien saw his boss as his constituents.

“If at any time I felt I couldn’t do the job, I’d leave in a minute,’’ O’Brien, 64, of Lynn, said in a phone interview Tuesday. “But I’m fully prepared to keep on going. ... I’m not going to sit home, is what I’m trying to say. I’m going to keep working. It’s the best thing in the world for me.’’

He said he plans to serve out his current term and seek reelection in 2018 to an office he has held since 1977.

As register, O’Brien is responsible for recording real estate transactions for 30 cities and towns in the southern part of Essex County.

His office described him as the first register to expose Wall Street and large banks for their practice of robo-signing mortgage documents in foreclosure proceedings.

When Lynn adopted an ordinance in 2013 to require banks to conduct face-to-face mediation with homeowners before foreclosing, O’Brien told the Globe he would not record any foreclosure deed from the city unless the bank had a certificate to prove it had done the mediation.

On Tuesday, Essex District Attorney Jonathan W. Blodgett, a longtime friend of O’Brien’s, praised him for revealing the bank practice of robo-signing and being one of the first officials to put real estate documents online for public view.

“John’s a very decent guy, and innovative in terms of how he’s run the registry,’’ Blodgett said. “He’s a good public servant.’’

He also lauded O’Brien for telling constituents about his diagnosis.

“It took a lot of courage on his part to disclose to the world that he’s got a serious condition,’’ Blodgett said. “I’m going to say a prayer for him and wish him all the best.’’

O’Brien said Tuesday that he decided to go in for tests after his daughter noticed his hands shaking.

“I was kind of shocked [by the diagnosis], to be honest with you,’’ he said. “It was time for me to let people know. I get tremors, there’s no question about it. I have a little bit of memory loss. It’s not something that’s effecting my ability to do my job.’’

On its website, the National Institute on Aging, a division of the National Institutes of Health, describes Lewy body dementia as “a complex and challenging brain disorder’’ with symptoms that can include muscle rigidity, slowed movement, loss of coordination, dizziness, memory loss, and hallucinations.

While O’Brien’s condition “currently cannot be prevented or cured, some symptoms may respond to treatment for a period of time,’’ the website says.

Lewy body dementia afflicts more than 1 million Americans.

In his statement Monday, O’Brien sounded eager to fight the onslaught of what can be a difficult condition.

“We get up each day and we keep on going, that’s what I’m going to do,’’ he said. “My hope is that we can all join together in bringing an end to this demon that can strike anyone at any time.’’

Travis Andersen can be reached at travis.andersen@globe.com. Follow him on Twitter @TAGlobe.