Paget's Disease of Bone Flashcards
Paget’s Disease of Bone Definition:
A common, benign metabolic bone disease characterised by the thickening and disturbance of architecture of the affected bone.
Bone Resorption
is resorption of bone tissue, that is, the process by which osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood.
Paget’s is characterised by:
Abnormal remodelling of bones:
•High rates of bone resorption
•The formation of disorganised immature new bone
•Increased Vascularity of affected bones
How common is Paget’s disease?
- Most common in Britain, then USA, Australia
- Rare before 50
Implicated viruses for Paget’s disease?
- Measles
- Respiratory syncytial virus
Paget’s Classification:
- Monostotic (15%)
* Polystotic (85%)
Bones most commonly affected with Monostotic Paget’s?
- Tibia
- Femur
- Skull
- Vertebrae
- Humerus
- Bone is in descending origin of frequency
Bones most commonly affected with Polystotic Paget’s?
- Spine
- Pelvis
- Femur
- Skull
- Sacrum
- Tibia
- Humerus
- Bone is in descending origin of frequency
Paget 3 Stages:
- Osteolytic Stage
- Mixed osteolytic-osteoblastic Stage:
- Osteosclerotic Stage
Paget’s Osteolytic Stage 1
- Irregular osteoclastic resorption of bone.
- Osteoclasts in affected bone are very large and contain micro-cylindrical inclusions.
- Normal bone is resorbed by abnormal osteoclasts
- The osteoclasts are more numerous, larger, & have more nuclei than normal (up to 100 c.f. 5-10 nuclei)
- Bone turnover rates increase to as much as 20 times normal
Paget’s Osteolytic Stage Lesions:
1•“Flame Lesion” of patchy radiolucency (lysis) extending along the shaft of the bone.
2•Flame Lesion= V lesion =Wedge lesion
3•The appearance of an osteolytic wedge advancing up or down the bone is typical in the Osteolytic phase when it occurs in a long bone
Paget’s Mixed Osteolytic-Osteoblastic Stage 2:
- Resorption is closely followed by new bone formation
- New matrix is haphazardly laid down mainly as woven bone ( haphazard organisation of collagen fibers and is mechanically weak)
- Bone resorption/formation are uncoupled i.e. don’t occur in a balanced faction (osteoblasts are making too much osteoid)
- As a result of the above:
•Mineralisation of matrix lags (laying down of bone cells on matrix that results in hardening and strengthening)
•Osteoid seams persist, demarcating the margins of the newly laid down bone.
•Tile-like or mosaic pattern of bone formation (pathognomonic)
•New bone is highly vascularised
•Adjacent marrow spaces fill with loose highly vascularised connective tissue. - Thus the conformation and internal architecture of the affected bone is changed.
- Bone volume remains approx. normal bone.
Paget’s Osteosclerotic Stage 3:
- osteoclastic activity may decrease, but abnormal bone formation continues. Osteoblast continue to keep making woven bone.
- After many years in the second stage, the condition “burns out”
Paget’s Osteosclerotic Stage Key Features:
- Formation of new bone which is:
- Disordered
- Poorly mineralised
- Poor structural stability
- Vulnerable to fracture
- Vulnerable to deformation
-Osteosclerosis (abnormal hardening of bone and an elevation in bone density)
Macroscopic characteristics
- Anterior bowing of femur and tibia
- Neck of femur sags to 90 degrees
- Skull is enlarged and irregularly thickened. Loss in differentiation between the diploe and tables
- Facial bones become coarse (leontiasis ossea)
