Scientists discovered that immune cells from psoriatic skin can migrate to the joints and ignite inflammation under the right conditions. Spotting these cells early could help stop psoriatic arthritis before it causes permanent damage. Credit: Shutterstock Roughly 20 to 30 percent of people with psoriasis eventually develop painful joint inflammation. This condition, known as psoriatic arthritis, can cause lasting damage to bones and joints if it is not treated. For years, doctors did not fully