Paget's disease is a bone condition that results in enlarged and deformed bones. It is a long-term condition. Any bone in the body can be affected. However, the most common sites are the spine, skull, pelvis, thighs, and lower legs.

Normal Bone Structure
Bone Matrix
Copyright © Nucleus Medical Media, Inc.

Paget's disease is caused by a malfunction in bone formation. Normally, bones are constantly being broken down and rebuilt. With Paget's disease, bones are broken down abnormally fast, and new bone replacement is loose and bulky, instead of strong and compact. These poorly formed bones may become weak. They also may bend over time.

The exact cause of this bone malformation is unknown. Paget's disease may be triggered early in life by a viral infection.