Pagets disease of bone (commonly known as Pagets disease or, historically, osteitis deformans) is a condition involving cellular remodeling and deformity of one or more bones. The affected bones show signs of dysregulated bone remodeling at the microscopic level, specifically excessive bone breakdown and subsequent disorganized new bone formation. These structural changes cause the bone to weaken, which may result in deformity, pain, fracture or arthritis of associated joints.The exact cause is unknown, although leading theories indicate both genetic and acquired factors (see Causes). Pagets disease may affect any one or several bones of the body (most commonly pelvis, tibia, femur, lumbar vertebrae, and skull), but never the entire skeleton, and does not spread from bone to bone. Rarely, a bone affected by Pagets disease can transform into a malignant bone cancer. As the disease often affects people differently, treatments of Pagets disease can vary. Although there is no cure for Pagets disease, medications (bisphosphonates and calcitonin) can help control the disorder and lessen pain and other symptoms. Medications are often successful in controlling the disorder, especially when started before complications begin. Pagets disease affects from 1.5 to 8.0 percent of the population, and is most common in those of British descent. It is primarily diagnosed in older people and is rare in people less than 55 years of age. Men are more commonly affected than women (3:2). The disease is named after English surgeon Sir James Paget, who described it in 1877.
A later phase of the disease is characterized by the replacement of normal bone marrow with highly vascular fibrous tissue.Sir James Paget first suggested the disease was due to an inflammatory process. Some evidence suggests that a paramyxovirus infection is the underlying cause of Pagets disease, which may support the possible role of inflammation in the pathogenesis. However, no infectious virus has yet been isolated as a causative agent, and other evidence suggests an intrinsic hyperresponsive reaction to vitamin D and RANK ligand is the cause. Further research is therefore necessary. Diagnosis
The first clinical manifestation of Pagets disease is usually an elevated alkaline phosphatase in the blood. Pagets disease may be diagnosed using one or more of the following tests:

Pagetic bone has a characteristic appearance on X-rays. A skeletal survey is therefore indicated. An elevated level of alkaline phosphatase in the blood in combination with normal calcium, phosphate, and aminotransferase levels in an elderly patient are suggestive of Pagets disease. Markers of bone turnover in urine eg. Pyridinoline
Elevated levels of serum and urinary hydroxyproline are also found. Bone scans are useful in determining the extent and activity of the condition. If a bone scan suggests Pagets disease, the affected bone(s) should be X-rayed to confirm the diagnosis.