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.
Pagets disease is uncommon in the native populations of North and South America, Africa, Asia, and the Middle East. When an individual from these regions does develop Pagets disease, there is typically some European ancestry present. History
The condition was initially described by Dr. James Paget. In a paper published in 1877, Paget told of five patients with "a rare disease of bones" which presented with slowly progressive bone deformities in the 4th and 5th decades of age. Strikingly, the first patient was described to have many of the classic complications of the disease, including arthritis related to abnormal bone mechanics, cranial nerve palsies associated with an enlarging skull, and malignant transformation of a tumor of the radius which ultimately proved fatal. Pagets post-mortem autopsy evaluation showed "bones of the vault of this skull were in every part increased to about four times the normal thickness," and microscopic evaluation showed evidence of both bone erosion and abnormal remodeling. Although he incorrectly attributed the findings to a process of chronic inflammation, having ruled out tumor and hypertrophy as alternative etiologies, these prescient observations of a mixed destructive/regenerative process correspond to the modern understanding of the disease. Holding, then, the disease to be an inflammation of bones, I would suggest that, for brief reference, and for the present, it may be called, after its most striking character, Osteitis deformans. A better name may be given when more is known of it.