Micrograph showing<unk> 's<unk>  of the<unk>  with the characteristic jigsaw puzzle-like/mosaic pattern, H&E stain The pathogenesis of<unk> 's<unk>  is described in four stages: # Osteoclastic activity # Mixed osteoclastic – osteoblastic activity # Osteoblastic activity # Malignant degeneration Initially, there is a marked increase in the rate of<unk>  resorption in localized areas, caused by large and numerous osteoclasts. These localized areas of pathological destruction of<unk>  tissue (osteolysis) are seen radiologically as an advancing lytic wedge in long<unk> s or the skull. When this occurs in the skull, it is called osteoporosis circumscripta. The osteolysis is followed by a compensatory increase in<unk>  formation induced by the<unk> -forming cells, called osteoblasts, that are recruited to the area. This is associated with accelerated deposition of lamellar<unk>  in a disorganized fashion. This intense cellular activity produces a chaotic picture of trabecular<unk>  ("mosaic" pattern), rather than the normal linear lamellar pattern. The resorbed<unk>  is replaced and the marrow spaces are filled by an excess of fibrous connective tissue with a marked increase in blood vessels, causing the<unk>  to become hypervascular. The<unk>  hypercellularity may then diminish, leaving a dense<unk> ic<unk> ," also known as burned-out<unk> 's<unk> . A later phase of the<unk>  is characterized by the replacement of normal<unk>  marrow with highly vascular fibrous tissue. Sir James<unk>  first suggested the<unk>  was due to an inflammatory process. Some evidence suggests that a paramyxovirus infection is the underlying cause of<unk> 's<unk> , 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.
Paget's disease of bone
Diffuse idiopathic skeletal hyperostosis
Albright's hereditary osteodystrophy
Giant-cell tumor of bone
Fibrous dysplasia of bone
Tumoral calcinosis
Metabolic bone disease
Oncogenic osteomalacia