Psoriatic (sohr-ee-AT-ick) arthritis, a less common form of arthritis, is a long-lasting condition that affects the skin and nails and produces joint inflammation. The disease usually affects people between the ages of 20 and 50. More than 80 percent of people with psoriatic arthritis have nail involvement, but the pattern of joint involvement varies widely. The disease is linked to psoriasis (SORE-eye-uh-sis), a skin disorder characterized by inflamed lesions (LEE-zhuns) with silvery or gray scales. Symptoms of psoriatic arthritis consist of scaly spots on the scalp, elbows, knees, and the lower back; stiffness, pain, and swelling in one or more joints; pitting of the nails characterized by small depressions or detachment of fingernails or toenails; and tenderness, pain, and swelling at sites where tendons and ligaments attach to the bone. The cause of psoriatic arthritis is unknown, but possible causes include heredity, infection, and perhaps, environmental factors. Although there's no cure for the disease, active involvement in a prescribed treatment plan is essential for easing pain and discomfort.