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Paget Disease of Bone (PDB), also known as osteitis deformans, is a chronic metabolic bone disorder characterized by abnormal bone remodeling due to excessive osteoclastic bone resorption followed by a compensatory but disorganized increase in osteoblastic activity. This leads to structurally weakened, enlarged, and deformed bones.

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https://www.youtube.com/watch?v=Gzi_Hr_vVMc

https://www.youtube.com/watch?v=NVcYG3_B8HU

https://youtu.be/S0Ne7vrmNTw

Etiopathogenesis

Etiology: Unknown; likely multifactorial with genetic (e.g., SQSTM1 mutations) and environmental (e.g., paramyxoviral infection) contributors

Disease phases:

Phase	Description
1: Lytic phase	↑ Osteoclast activity
2: Mixed lytic and sclerotic phase	Both osteoclast and osteoblast hyperactivity
3: Sclerotic phase	Dominant osteoblastic activity, bone thickening but disorganized
4: Burnt-out phase	quiescent phase

Epidemiology

Parameter	Description
Age	>50 years
Sex	Slight male predominance
Prevalence	Common in Western Europe, rare in Asia

Clinical features

Manifestation	Description
Asymptomatic	Most cases detected incidentally
Bone pain	Due to microfractures, deformities
Skeletal deformities	Bowing of long bones, skull enlargement (“hat size” increases)
Fractures	Pathologic fractures, especially in the femur or tibia
Neurologic symptoms	From compression (e.g., hearing loss due to skull involvement)
High-output cardiac failure	Rare, in extensive polyostotic disease due to AV shunts

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Disease distribution:

Disease forms	Prevalence	Predilection
Monoostotic disease	10-35%	Axial skeleton (frequently unilateral)
Polyostotic disease	65-90%	Right-sided predominance, usually the lower extremities

Common sites:

Pelvis (M/C, 30-75%)