From Carol & Richard Eustice,
Your Guide to Arthritis.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

There are over 100 types of arthritis. What are the differences in the clinical picture of psoriatic arthritis and rheumatoid arthritis, other than the obvious additional symptoms of the skin disease psoriasis?

A. Joint inflammation and stiffness in patients with Psoriasis, and RA share a common feature. Both conditions are caused by an erosive inflammatory arthritis. The distribution of joint involvement however, differs between the two diseases. Classic RA is a symmetrical disease primarily involving the PIP joints and wrists. RA nodules are often present. Psoriasis is an asymmetric disease most often causing "sausage deformities" of the digits, and deformities of the DIP joints of fingers and toes involved with psoriatic nail changes. Typically, skin lesions are associated with Psoriasis. Sometimes proliferative synovitis of the wrists and fingers occur, resembling RA. In these cases, x-rays and laboratory testing help to differentiate the two diseases. Treatment for both conditions are similar, using anti-inflammatory agents, anti-malarials, and adding Methotrexate for stubborn cases. (Answer provided by the late Dr. Raymond Federman, aka Dr. Bones, who passed away on September 2, 2003. The care of his patients even in retirement was always his joy.)