Nearly three years ago, U.S. Sen. Johnny Isakson’s son Kevin noticed that his father’s left arm did not swing when he walked.

Internet research and doctor’s visits confirmed that the Georgia Republican has early-stage Parkinson’s disease, a diagnosis he revealed for the first time Wednesday and one that Isakson said will not deter him from running for re-election next year and serving a full six-year term.

Isakson, 70, has shown limited symptoms so far — a stiff arm and a shuffling gait — and got medical clearance to keep up his aggressive schedule.

“Parkinson’s, you have two choices: You can let it control you, or you can control it. And I’ve chosen to take control of it,” Isakson told reporters in his Capitol Hill office.

The personally and politically fraught announcement included a news media phone call with Isakson’s neurologist, Dr. Thomas M. Holmes of Marietta.

“I don’t see any reason at this point that he would have to slow down or that it would be detrimental to his disease process,” Holmes said. “Some motor symptoms may worsen over a seven-and-a-half year period. …

“I believe he will be able to maintain his schedule and his duties as a senator, and a part of that is seeing how he’s responded so far to treatment and how vigilant he has been both with medications and physical therapy.”

Disease was diagnosed in 2013

Isakson was first diagnosed in August 2013 and most recently saw Holmes last month. He is at stage 1.5 of the five-stage disease, Holmes said, adding that Isakson has shown no cognitive problems and the 25- to 30-year course of the disease probably will not shorten his life.

There is no cure, but Isakson has been containing symptoms with a dopamine patch and the generic version of the common Parkinson’s drug Sinemet.

Isakson’s health has been a frequent source of concern and speculation in Georgia political circles. In 2010, he spent time in the hospital twice with a bacterial infection but still won re-election that year with ease.

He announced in November that he would seek a third term, as early as possible in the election cycle to get ahead of talk that he would retire. Isakson had back surgery in October and cracked three ribs this spring.

The worsening shuffle was also noticeable to those around him.

“People over time were able to tell he was struggling a little more physically, but now it makes sense,” said Chip Lake, a Georgia Republican political consultant.

Re-election campaign progresses

Lake said “strictly speaking politically, (the announcement) could help him.” But he added that Isakson will need to continue to “raise money aggressively so that those Republicans or Democrats that might be speculating on whether or not he runs again will be looking at those numbers.”

Through March, Isakson had $3.75 million in his campaign bank account, well ahead of his pace from the last cycle.

Athens-based Republican strategist Joel McElhannon called the diagnosis “heartbreaking” and offered his prayers. But he agreed there is a political benefit: “Who wants to be the jerk running against a Georgia icon dealing with a difficult disease?”

Isakson so far has one declared opponent: Stone Mountain minister and MARTA engineer Derrick Grayson, who offered "thoughts and prayers" to Isakson and his family on Twitter, but he also reminded followers of his challenge to the senior senator and sent a mass email about a forthcoming fundraiser.

Democrats are still trying to recruit an opponent, though several of the party's big names have said they are staying out of it, given Isakson's political strength.

Support from both sides of the aisle

In Washington and Georgia the announcement sparked an outpouring of well-wishes and encouragement from both parties. Known as a gentlemanly deal maker, Isakson has risen to chairman of the Ethics and Veterans Affairs committees.

“No one works harder than Johnny Isakson, who is the only senator who is chairing two committees in the Senate,” said Majority Leader Mitch McConnell, R-Ky. “This diagnosis will not slow him down one bit.”

Added Minority Leader Harry Reid, D-Nev.: “Senator Isakson is tough. … Today’s announcement has shown his tremendous courage in his fight against Parkinson’s and his resolute determination to not let it take control of him.”

Isakson: Limitations ‘ones you place upon yourself’

Doctors say another term is reasonable

Parkinson's is a brain disease that affects an estimated 7 million to 10 million people worldwide, including boxer Muhammad Ali and actor Michael J. Fox.

A pair of experts backed up the assertion by Isakson’s doctor that the senator could run and serve effectively for seven-plus years, though he could develop tremors or other more advanced physical symptoms.

Cognitive problems typically appear “much later in the disease,” said James Beck, the vice president of scientific affairs for the Parkinson’s Disease Foundation.

Dr. Stewart Factor, the director of the Emory University School of Medicine’s Comprehensive Parkinson’s Disease Center, said: “Progression is variable, so where he would be five years down the road is difficult to predict, but I don’t think it’s unreasonable to think that he could” serve out another term.

Holmes said that it would not make sense to slow down. In fact, it helps Isakson to keep giving speeches, attending fundraisers and working on legislation, all while commuting from Atlanta to Washington each week.

“I try to encourage patients to continue their typical activities,” Holmes said. “Frankly, I think that’s part of what keeps each one of them going, including Senator Isakson.”

As evidence of his continued effectiveness, Isakson pointed to a pair of policy wins in the past week: South Africa's agreement to drop tariffs on U.S. poultry and movement on compensation for the 1979 Iran hostages.

Isakson said he takes special solace in the story of astronaut Rich Clifford, who went into space after his Parkinson's diagnosis. The senator was his typical upbeat self during his session with reporters, jumping out of his seat to greet them.

“There are a lot of misconceptions about its limitations,” Isakson said of the disease. “Its limitations are primarily the ones you place upon yourself, not the ones it places on you.”

He cut off a well-wisher who offered a “feel better.”

“This isn’t a feeling-bad disease,” Isakson said. “I don’t feel bad. I feel good. I’m a James Brown guy.”