Phil Mickelson Arthritis: Will Play At PGA Whistling Straights

"I have no aches and pains," Mickelson recalls saying. "My back feels great. I feel stronger and more flexible than I've ever been."

Several days later as his preparations for the U.S. Open intensified, though, Mickelson started waking up in a world of pain. His Achilles throbbed. His left index finger felt like it was sprained, and so did his right wrist.

Joint pain, stiffness and swelling are the main symptoms of psoriatic arthritis. They can affect any part of your body, including your fingertips and spine, and can range from relatively mild to severe. In both psoriasis and psoriatic arthritis, disease flares may alternate with periods of remission. No cure for psoriatic arthritis exists, so the focus is on controlling symptoms and preventing damage to your joints

Mickelson said the psoriatic arthritis quickly spread from his ankle, finger and wrist to his hips, elbows and shoulders.

"He is not being dramatic; that can literally happen to someone experiencing a flare of psoriatic arthritis," said Michael Paranzino, president of the nonprofit Psoriasis Cure Now.  "One day you are feeling fine, and days later it can be difficult to get out of bed or tie your shoes. Psoriatic arthritis is a serious disease."