Psoriatic arthritis is caused by an overactive immune system. It affects the joints, often those in the fingers or toes.
The impact of psoriatic arthritis varies greatly from one person to another, depending on how many joints are involved, says Nortin Hadler, MD, a rheumatologist and professor of medicine and microbiology/immunology at the University of North Carolina at Chapel Hill.
Still, no matter how bad the disease, early diagnosis and treatment helps. Here are the stories of four people who have grappled with psoriatic arthritis.
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Pro golfer Mickelson thought the pain near his ankle and in his left index finger and right wrist were a result of practicing and playing.
But within days the aching and stiffness got so bad he could barely haul himself out of bed.
A rheumatologist diagnosed Mickelson with psoriatic arthritis, just several years after the star started to experience symptoms of psoriasis, a related skin condition. As a result of early treatment for psoriatic arthritis, he has regained 20% of the strength he lost the year he was diagnosed, he told USA Today.
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The pianist was a child prodigy at age 4 and a protégé of the great Vladimir Horowitz. For years he concealed his psoriatic arthritis, which he developed in 1973, by altering his playing style.
In 1985, Janis went public. Acupuncture and medications helped him, and he had a series of surgeries to restore movement to his hands and wrists. Janis told ABC, "Arthritis has taught me to look inside myself for new sources of strength and creativity. It has given my life a new intensity. I have arthritis, but it does not have me."
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Considered by some to be the greatest guitarist of all time, Lane had to cope with psoriatic arthritis almost from the time he started playing. He reportedly developed a severe form of the arthritis at age 13 after an early-childhood diagnosis of psoriasis. (About 10% of people who have psoriasis go on to develop psoriatic arthritis.)
Lane was able to keep playing guitar and piano but had trouble walking. The steroids he took to control his condition caused him to gain weight (at one point he weighed more than 300 pounds). He died in 2003 of pulmonary fibrosis, which is a scarring of the lungs that occurs in some people with psoriatic arthritis.
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British dramatist Potter, who died in 1994, suffered from severe psoriatic arthritis that was crippling at times. Potter was in and out of hospitals after his diagnosis, and his hands, he once said, were whittled down to "clubs."
He continued to write by fastening a pen to his hand. His BBC series The Singing Detective, for which he is best known, featured a writer with psoriatic arthritis who also ends up having to write with a pen tied to his hand.