Golfer Phil Mickelson was the No. 2-ranked player in the world when he   revealed that he is battling psoriatic arthritis, an inflammatory form of arthritis that came on suddenly and left him temporarily in a near-crippled state this summer.

Mickelson said he first noticed symptoms, including searing pain, in the days leading up to the U.S. Open in 2010.

After a trip to the Mayo Clinic in Rochester, MN, Mickelson began taking weekly injections of etanercept (Enbrel), an injected, biologic drug that helps to lower levels of a protein that spurs inflammation.

In the days leading up to last week’s PGA Championship, the year’s last major golf tournament, Mickelson first talked about his arthritis and said he was pleased with how he was responding to medication.

“I feel great,” he said to a group of golf reporters. “I’m able to work out and don’t have any pain. So I’ve had some good immediate response. And that’s why I feel comfortable talking about it, knowing that long term and short term, things are fine.”

Psoriatic arthritis is not the first serious medical issue that the Mickelson family has had to face. Mickelson took most of 2009 off after his wife Amy was diagnosed with breast cancer. Already a fan favorite, he became even more popular for the way he stepped away from the game to take care of his family. Mickelson came back this year and won The Masters in April.

It was soon after that he began to experience mysterious pain and stiffness.

Psoriatic arthritis (PA) is an autoimmune disease, meaning that the body’s immune system attacks its own organs and tissues. The condition is rare, affecting about 1 out of 100 people in the general population. People with psoriatic arthritis not only have joint pain, but also experience plaque psoriasis, a red scaly rash that commonly appears on the skin of the arms and legs, scalp, palms and the soles of the feet. Over time, psoriatic arthritis can lead to permanent joint damage and disability.

The fact that he was even able to play golf, much less compete in a couple of major tournaments with this condition, is amazing, says Robert Shaw, MD, a practicing rheumatologist and instructor of medicine at Johns Hopkins University in Baltimore.

“It clearly shows what an elite athlete he is,” Dr. Shaw says. “People with PA sometimes have trouble dressing themselves. He could have had a milder case of it, but eventually, untreated, it still overtakes you. You can’t just move on. The hallmark of this type of inflammatory arthritis is that it causes you to stiffen with even minutes of rest. So if he takes a short water break while playing, his joints would stiffen up.”

Enbrel is one of four “big-gun” medications used to treat PA, and Dr. Shaw says that for some people they are almost miracle drugs.