SHEBOYGAN: Golfer Phil Mickelson revealed on Tuesday he has been diagnosed with a severe form of arthritis that attacks the body`s immune system and in his case left him unable to even get out of bed.

The reigning Masters champion said doctors at the Mayo Clinic in Minnesota are treating him for psoriatic arthritis which first flared up in the week prior to the US Open.

"I have this thing called psoriatic arthritis where your immune system attacks your joints and tendons and so forth," Mickelson told reporters at the Whistling Straits golf course where he is set to compete in the 92nd PGA Championship which starts Thursday.

"It is very treatable and the medicine I`ve been taking has been very helpful. I feel 90 percent."

This is just the latest in a series of misfortunes to hit the Mickelson family.

He has taken a number of breaks from the PGA Tour over the past year to help his wife and mother who are both battling breast cancer.

If he goes ahead and competes this week, the world number two could surpass Tiger Woods for the top spot with a strong performance at the final major championship of the 2010 season.

The left-handed American had a chance to overtake Woods last week but still feeling the effects of his newly-diagnosed disease stumbled to a final round 78 at the World Golf Championships Bridgestone Invitational.

Remarkably Mickelson also played well enough at this year`s US Open to give him a shot to win despite the initial onset of the disease.

"I am about back to 80 percent of the weight weight I was at before so things look good," he said. "I am not sure where I will be on Thursday but hopefully I will be ready."

Mickelson first visited his physician but then decided to get another opinion from the doctors at the Mayo Clinic in Minnesota.

"About eight weeks ago, about five days before the US Open I woke up and had some intense pain in some areas of my body, some joints and tendons and so forth. I couldn`t walk," Mickelson said. "I ended up going and seeing a doctor and I ended up going back to the Mayo Clinic right after the British Open to get a second opinion.

"Everything is fine now. I have been starting treatment and things have been great.

"Long term there shouldn`t be any issues. It is very treatable and the medicine I have been taking has been very helpful. I feel 90 percent."

Doctors don`t know what causes psoriatic arthritis but treatment can involves taking anti-inflammatory drugs and steroid injections.

In some cases surgery is needed to fix or replaced damaged joints.

BDST: 1357HRS, August 11, 2010