Psoriatic arthritis is a systemic rheumatic disease that also can cause inflammation in body tissues away from the joints other than the skin, such as in the eyes, heart, lungs, and kidneys. The cause of psoriatic arthritis is currently unknown. Precisely defining psoriatic arthritis is still difficult because of a lack of specific biologic tests. If you belong to the 85% of psoriatic arthritis patients who have already had psoriasis of the skin, scalp, or nails diagnosed, the diagnosis may not be too difficult to obtain. The main risk factors for psoriatic arthritis are family history, age, and gender. Though typically mild, this form of psoriatic arthritis can be debilitating in some cases.