Musculoskeletal and Skin Pathology for Medical II Students

Lab 1d Paget Disease of Bone/Osteitis Deformans (11000-76570)

Paget disease is a bone disorder usually occurring in older patients, and characterized by disordered bone cell activity. The histologic appearance varies depending on the state of activity of the disease. There is an:

• initial osteolytic phase
• active stage of mixed osteolysis and osteogenesis and
• inactive (sclerotic) phase. 

The initial stage shows increased osteoclastic bone resorption. The active stage of mixed activity shows prominent osteoclasts and osteoblasts. The normal bony structure is destroyed, followed by irregular bone formation that results in a pathognomonic "mosaic" pattern with persistent osteoid seams (cement lines). The thickness of the bone is increased but the bone is soft and poorly mineralized. In the inactive stage, the thickened bone with the mosaic pattern of cement lines remains, but there is little osteoclastic or osteoblastic activity in multiple bones. A laboratory feature characteristic of the active phases is marked elevation of the serum alkaline phosphatase that reflects increased osteoblastic activity. Complications of Paget disease of bone include pathologic fractures (fairly common), high out put heart failure and the development of sarcoma (rare). The sarcoma is usually osteogenic sarcoma. When an older patient develops osteogenic sarcoma, consider the possibility that there is underlying Paget's disease of bone.

Slides 16 & 17 | Slide 18

Slide 18 An older lesion. Note that there is no normal Haversian system, but that the different remnants of the Haversian systems, recognizable by the bone lamellae, are fused by osteoid formation around canaliculi. Although the process of decalcification affects the staining of the section, the observant student can see evidence that the bony changes are caused by repeated episodes of osteolysis and excessive efforts at replacement. With regular illumination, examination of some of the spaces containing blood vessels and fibrous tissue will reveal osteoclasts and osteoblasts, suggesting residual activity. Under the microscope, reducing the light by closing the iris of the condenser will help in seeing the extent of the aberrant rebuilding of bone that results in irregular fusion lines between the osteons (the "mosaic" pattern).

Digital Legends for Labs/Cases
Lab 1
1a | 1b | 1c | 1d | 1e | 1f | 1g
Gross & Radiographs
a | b | c | d | e | f | g | h 
Lab 2
2a | 2b | 2c | 2d | 2e | 2f

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Updated January 15, 2008