At its worst, Phil Mickelson’s Achilles heel was on fire, his knees and hips ached and his shoulder hurt so much that he could not lift his arm above his head.

Arguably the world’s most beloved golfer – and the winner of three Masters championships – Phil worried that his career might be over. He knew this for sure: The debilitating pain, almost crippling at times, was not the normal aches and pains of a 40-year-old athlete.

Something was seriously wrong.

“There was a lot of uncertainty,” Phil says. “I was pretty worried. I didn’t know about the long-term future; I didn’t know what my immediate future held. The mind tends to wander. Mine certainly did.”

And the mind started its racing: What is wrong with me? Whatever it is, is it treatable? Is my career over?

Just a year earlier, Phil’s wife, Amy, and his mother, Mary, had been diagnosed with breast cancer. So when his mind wandered, it tended to head toward worst-case scenarios. But what Phil was about to learn left him with more questions than answers.

Two doctors, his general practitioner in California and a rheumatologist at the Mayo Clinic in Rochester, Minn., told him he had psoriatic arthritis, an autoimmune disease in which the body’s immune system attacks the joints. Arthritis of any kind – and there are more than 100 types – is not a welcome diagnosis for anyone. For a professional golfer who makes a living contorting his body with powerful torque, it’s that much worse.

“They told me that this kind of arthritis was one of the more treatable ones,” Phil says, “but there were no guarantees.”

Since announcing that he had psoriatic arthritis last August, just before the start of the PGA Championship, Phil has remained quiet about his condition and the effects it was having on his golf game and his life as an active husband and father. But Phil opened up recently to Arthritis Today about the time leading up to his diagnosis and what he thinks his future will look like.

His Achilles Heel

“It’s been a tough couple of years and I had just gone through the most emotionally stressful time of my life with Amy’s cancer diagnosis,” Phil says. “The way that she took on her illness was inspiring and it sparked me to take on mine without delay, and that turned out to be very important to stop what could be permanent damage.”

Severe stress can be a trigger for psoriatic arthritis, says Eric Matteson, MD, Phil’s rheumatologist and chair of Mayo Clinic’s rheumatology department. But it doesn’t cause it. Experts think the disease is caused by having a genetic pre-disposition that is set off by an environmental trigger – say, infection, smoking or even extreme stress.

What Phil now knows is that he’s had the disease in a mostly dormant state for years. He had what he thought were the normal aches and pains of an athlete who was getting older. And there was something else – something so seemingly insignificant that he’d never given any real attention to. He occasionally had a flaky, itchy scalp.

Both are telltale signs of psoriatic arthritis, a disease that flared for the first time in Phil a week before the U.S. Open last June.

“I was in excruciating pain in the Achilles heel and the back of my legs. That first morning, I couldn’t get up. After two or three hours, I finally got it stretched out to where I could function. But as soon as I was off my feet for an hour or so, it came right back. I hadn’t experienced that kind of pain before.”

Phil played the U.S. Open in that condition.

“The best thing you can say about Phil Mickelson’s first round at the U.S. Open is that no children or animals were harmed in its making,” wrote an ESPN columnist in describing Phil’s day one play.

Phil rebounded and stayed in contention for most of the tournament. But he was hurting and was not at his best. It got worse before getting better.

“Four days after the U.S. Open, we went on a family vacation to Hawaii, and at night, the pain was so intense that I couldn’t move. I had no idea arthritis could be that debilitating. I didn’t know much about it at all.”

Getting Worse

When Phil got back to his California home, he made an appointment with his doctor, who put him on a steroid pack. Most of the pain subsided. But as soon as the steroid regimen was done, the pain returned.

“He felt we had a problem then, and diagnosed me with psoriatic arthritis. I went to the Mayo Clinic and got the same diagnosis.”

By this point, the pain that had begun in his heels had progressed to the hips, knees and shoulders.

“Swinging a golf club was not an option at that point,” he says. “I couldn’t even take it back halfway. That was pretty worrisome.”

Dr. Matteson says that worry – both pre- and post-diagnosis – is common. And not unmerited.

“Psoriatic arthritis is not as benign of a disease as was once thought,” he says. “It’s not milder than rheumatoid arthritis, or RA. If you start treatment early, you can reduce a lot of the [joint] damage and keep people functional most of the time. But when your livelihood depends on your physical abilities, it is very concerning.”

Not only that, Dr. Matteson says, if left untreated, the disease can cause problems in the heart, eyes and other organs and ultimately shorten life expectancy.

“Often what we see is, by the time a patient comes to the clinic, they have evidence that joint erosion has taken place,” Dr. Matteson says. “Starting treatment early is huge.”

Phil tried taking prednisone, but the side effects were awful, he says. Then doctors at the Mayo Clinic prescribed weekly injections of a biologic drug that blocks TNF-alpha, an immune system protein that drives up inflammation. Biologic medications, including adalimumab (Humira), etanercept (Enbrel), infliximab (Remicade) and golimumab (Simponi), can be very effective for autoimmune diseases like psoriatic arthritis and RA, but Dr. Matteson says they don’t work for everyone and they do have risks. Because they suppress the immune system, people who take them are at risk of serious infections.

New Game Plan

Phil didn’t pick up a golf club for about six weeks. In early January of this year, he started practicing again with his world-renowned coach, Butch Harmon. The two have laid out a game plan that Phil believes can put him back at the top of his sport.

Even though Phil won the Masters green jacket in 2010 – and a $1.35 million purse – his year wasn’t what he had hoped for.

“I was excited about how I ended 2009 and had expected 2010 to be a great year,” he says. “I think my best golf may still be ahead of me, that 2011 can be the year I thought 2010 was going to be.”

For PGA golfers at his level, January through March is a 12-week tune-up for the Masters Tournament, the first of the four major golf tournaments. But Augusta National, where Phil has won three times, is an unforgiving course. Currently the No. 4 ranked golfer in the world, Phil knows that come April, he’ll have to be at his best to defend his championship against the likes of Tiger Woods, Lee Westwood and Jim Furyk, and win for a fourth time there.

“I like where I am physically and am optimistic about 2011,” he says.

When Phil was fresh off the diagnosis and initial treatments, he talked about taking the biologic injections for a year or so, then being done with it. He now understands that his expectations were unrealistic.

“My condition is something that’s going to be part of my life from here on out,” Phil says. “From what I understand, this disease, or its effects, will come and go for the rest of my life. I might take medicine for a year and then go off of it. Then, when and if it flares up, I’d go back on the medicine. I’m OK with taking medicine the rest of my life if I have to.”

Dr. Matteson says remission – not a cure – is the goal right now. “These are ongoing problems that have to be managed on a continuing basis. You think it’s gone because the symptoms have quieted, then it flares up. In that sense, it’s like a forest fire.”

Bill Sanders, a freelance writer living in Atlanta, has covered six Masters Tournaments.

This interview took place after Phil Mickelson entered into a partnership with Amgen-Pfizer, an Arthritis Foundation sponsor, in November, 2010.