The cause of Paget's disease is unknown. It may be due to genetic factors or a viral infection early in life.
The disease occurs worldwide, but is more common in Europe, Australia, and New Zealand.
In people with Paget's disease, there is an abnormal breakdown of bone tissue in specific areas. This is, followed by abnormal bone formation. The new area of bone is larger, but weaker. The new bone is also filled with new blood vessels.
The affected bone may only be in one or two areas of the skeleton, or throughout the body. It more often involves bones of the arms, collarbones, leg, pelvis, spine, and skull.