Paget's disease of bone occurs when your body replaces old bone tissue too quickly, leading to irregularly shaped bones. These bones can be bent, weak, brittle, soft, or too large. Commonly affected areas include the pelvis, skull, spine, and legs. The disease can cause bone fractures and other health issues, such as pressing on nerves or causing arthritis. It is most common in people over 40, particularly men. The exact cause is unknown, but it may be linked to viral infections, environmental factors, or genetics. Symptoms develop slowly and might include bone pain, arthritis, and visible bone changes. In severe cases, it can cause bone cancer or heart failure. Diagnosis usually involves blood tests and X-rays. While there is no cure, treatments can help manage symptoms and complications. Surgery may be needed for fractures or severe deformities.