Epidemiology and Etiology

Males are more at risk from Paget's disease than are females by a 3:2 ratio. There is evidence of heritabil-ity: A survey, for example, revealed that 13.8 percent of patients with Paget's disease had relatives with Paget's disease. Approximately half were from successive generations and half from siblings. Familial cases had an earlier onset than did isolated cases. An autosomal dominant pattern was suggested.

The etiology remains unknown. Paget named this disease "osteitis deformans" in the belief that the basic process was inflammatory and had an infectious origin. Recent ultrastructural studies of involved bone have revealed nuclear and cytoplasmic inclusions. They have not been found in bone cells of patients with other skeletal disorders, with the exception of giant cell tumors of bone. Morphologically the nuclei resemble those of cells infected with paramyxoviruses such as parainfluenza, mumps, and measles, and the cells resemble cultured cells infected with respiratory syncytial virus (RSV).

This tubular morphological finding has raised the question as to whether Paget's disease is a slow virus infection of bone. Other slow virus infections of human beings have similarly demonstrated a long clinical latent period, absence of an acute inflammatory response, a slowly progressive course, restriction of disease to a single organ system, patchy distribution in the body, and genetic predisposition.

Immunohistological studies of bone biopsy specimens have demonstrated antigen from RSV and measles. An indirect immunofluorescence antibody assay has demonstrated evidence for both measles and RSV antigens in Pagetic bone grown in culture from 30 patients. The suggestion of different RNA viruses (measles is a member of the genus Morbillivirus, whereas RSV is a member of the genus Pneumo-virus) seems incompatible. It has been proposed that Paget's disease stems from a previously uncharac-terized virus, perhaps of the Pneumovirus group. According to this hypothesis, Paget's disease patients are infected with a slow virus at an early age, probably under the age of 30. The slow virus isolates to particular areas of the skeleton by growth pattern and/or blood supply. As the metabolic activity of the skeleton decreases with age, the infested osteoclasts increase their metabolic activity, eventually producing diseased bone some 20 to 40 years following the initial infestation.

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