Cause

We don't know what causes Paget's disease. But genetic factors and viruses may play a role.

• Genetics. If your parents, brothers, or sisters have Paget's disease, you are more likely to develop the disease than if you do not have a family history of the disease.¹
• Virus. Viruses have been found in the bones of people with Paget's disease. The viruses may be associated with measles or canine distemper (found in dogs).² But there is no proof that any of these viruses cause Paget's disease.

Symptoms

Most people with Paget's disease have no symptoms. When there are symptoms, the most common are bone pain and bone deformities. People may have these symptoms for years before they are diagnosed as having Paget's disease.

Paget's disease usually affects the bones in the pelvis, spine, thigh (femur), skull, shin (tibia), and upper arm (humerus). One bone (monostotic) or several bones (polyostotic) may be affected by Paget's disease.

Bone pain

Paget's disease may cause warmth, tenderness, and pain in the affected area. The bone pain tends to be worse at night and often can keep you awake. The pain does not increase when you move the affected bone and may get better with exercise. Because this pain is often aching and hard to describe, you may think it is part of the aging process. Some people who have Paget's disease describe the pain as constant and deep.

The amount of bone pain may not relate to how much damage the disease is causing. You can have Paget's disease without having much bone pain, or the disease may be less severe but cause you a great deal of pain. Bones are often more painful when bone tissue is being broken down during active Paget's disease than at other times in the disease process. Pain may also be caused by a complication of Paget's disease, such as arthritis.

Bone deformities

Paget's disease may lead to bone deformities such as bowed legs, an enlarged skull or hips, or a curved backbone. Deformities are more common in long bones, such as the thighbone (femur).

A bone affected by Paget's disease can cause complications. For example, if the upper leg bows, it may change how the bones that form the hip joint and knee joint fit together and move, leading to osteoarthritis. Osteoarthritis, in turn, can cause pain and stiffness in the joints and difficulty with walking and other daily activities.

Other symptoms may occur as the result of the location of Paget's disease. For example, the disease can affect the skull and cause headaches, dizziness, loss of facial muscle strength (facial droop), or problems with vision or hearing. When Paget's disease affects the spine, it can damage nerves and cause leg pain, numbness, weakness, or cauda equina syndrome (an emergency condition with symptoms that include loss of feeling in the pelvic area and legs).