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.