Paget disease (osteitis deformans) is a localized disorder of bone remodeling, result-ing in excessive bone resorption followed by disorganized bone replacement, pro-ducing thickened but weak bone that is susceptible to deformity and fracture. There is an association with paramyxovirus and mutations of SQSTM1.
• Seen in those age >40
• Common in those of European ancestry
• Common sites of involvement include the skull, pelvis, femur, and vertebrae
• Majority of cases are polyostotic and mild
Paget disease develops in 3 stages:
• Osteolytic stage (osteoclastic activity predominates)
• Mixed osteolytic-osteoblastic stage
• Osteosclerotic stage (osteoblastic activity predominates in this “burnout stage”)
Paget disease can cause bone pain and deformity, fractures, and warmth of the over-lying skin due to bone hypervascularity. X-rays show bone enlargement with lytic and sclerotic areas. Lab studies show highly elevated serum alkaline phosphatase and increased levels of urinary hydroxyproline. Complications include arteriove-nous shunts within marrow, which may result in high-output cardiac failure and an increased incidence of osteosarcoma and other sarcomas.
Microscopically, there is a haphazard arrangement of cement lines, creating a “mosaic pattern” of lamellar bone. Involved bones are thick but weak and fracture easily. Skull involvement leads to increased head size and foraminal narrowing that can impinge on cranial nerves, often leading to deafness. Involvement of facial bones may produce a lion-like facies.
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