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Paget's disease (Ostetitis Deformans)
Paget disease
General Information
Paget's disease (ostetitis deformans) is a disease of hyperactive, unregulated giant osteoclasts. It results in increased bone resorption and disordered bone mass formation. It typically begins after 50 years old and most individuals are asymptomatic (it’s identified incidentally on X-Ray imaging). However, it can manifest with a variety of findings including skull thickening, hearing loss (from cochlear changes), bone fractures, tibia bowing ("saber shin"), heart failure, and many other complications.
Etiology
It’s thought to be secondary to latent viral infection in genetically susceptible individuals.
Pathology
General
A classic mosaic pattern is observed due to the breakdown and rebuilding that occurs in the disease process.
Phases
Initial: osteolytic phase
- Osteoclasts are the prominent finding – they break down the bone.
- Both osteoclasts (early) and osteoblasts (late) are present.
- Osteoblast activity dies-down and there is prominent sclerosis.
- The bone has a disordered, jigsaw-like pattern from the prominent cement lines, which makes it thick but unstable.
- There’s thick cortical bone and the trabecular bone is coarse with mixed sclerotic and lytic regions: marked widening and enlargement of the bones.
Skeletal involvement
Single vs Multiple
Monostotic - Single bone
Polyostotic - Multiple bones
Common Sites
Skull, vertebral bodies, pelvis, and long bones.
Clinical Complications
Various skeletal and non-skeletal complications occur due to this bone disease
- Bone pain
- Osteosarcoma, which is rare but life-threatening.
- Association with hyperparathyroidism
- Chalk-stick fractures (especially in the long bones of the lower limbs – so-named for it's chalk-stick or carrot stick snapped appearance).
- Bending deformities of affected bones (eg, the tibia bows forward (saber shin)).
- Heart failure because the hypervascular bone drives forms a shunt, in essence, thus there is a high-output heart failure that can arise through increased blood flow.
- Skull thickening
- Think of a lion's head to remember that a syndrome of lion-face (leontiasis ossea) can occur where the skull thickens so greatly it's hard to hold upright.
- This bone thickening can lead to platybasia (flattening of the skull base) and ultimately basilar invagination (where the odontoid tip projects up into the foramen magnum).
- Posterior fossa compression results from the heavy head and one can easily imagine how this can manifest with compression (crushing) of exiting cranial nerve roots and additional neurological manifestations (for instance, hearing loss from bony destruction).
- Nerve root compression from bony enlargement and compression.
Diagnosis
X-Ray demonstrates osteolytic and osteosclerotic lesions.
Alkaline phosphatase levels are elevated with normal calcium and phosphate.
Treatment
No curative treatment. Goal is to reduce pain and try to reduce progression with bisphosphonates (or calcitonin), calcium with vitamin D, pain meds.
Helpful Mnemonic (Summary)
BIG LIONS Have Heart failure
- Bone pain
- Increased bone density
- Giant osteoclasts
- Lion face
- Increased alkaline phosphatase
- Osteolytic and sclerotic lesions on X-Ray
- Nerve compression
- Saber shin
- Hearing loss
- High output Heart failure