Holes appear in bones replacing normal bone with scar tissue and extra blood vessels.
Usually a person has no symptoms whatever and an X ray shows the boney changes. Sometimes, a person breaks a bone and the x ray shows that the holes in bone due to Paget's disease caused the break. A routine blood test can show high blood levels of an enzyme called alkaline phosphatase, causing a doctor to order special x rays called a bone scan that picks up the disease, and lastly a person may have bone pain that prompts the doctor to order x rays of bone. Nobody really knows what causes Paget's disease, but most physicians feel that it is a passing infection in bone, and the most likely cause is paramyxoviruses. No treatment is needed when a person has no pain and no weakening of bone that is likely to result in fractures.