Definition

• Paget disease is a chronic metabolic bone disorder characterized by imbalance between bone resorption & new bone formation.

• It is chronic metabolic bone disorder characterized by abnormal osseous remodelling.

Incidence

• It is common in England.

• It is uncommon in Egypt and Middle East.

• Age: it affects older persons.

• Sex: more common in males.

Etiology

• Unknown.

• but recent hypothesis claims that it is due to slow virus infection (due to the presence of intranuclear inclusion bodies in the osteoclasts).

Pathology

Paget disease is divided into 3 phases:

1. Hot phase.

2. Intermediate phase.

3. Cool phase.

These 3 phases represent a continuum not separate phases.

Hot

phase

Osteolytic phase

Incipient phase

Osteoclasts predominate

& cause bone resorption.

Intermediate phase

Mixed phase

Active phase

Osteoblasts

cause bone repair superimposed on bone resorption.

Cool

phase

Blastic phase

Non active phase

Osteoblasts predominate

& cause new bone formation.

C.P

Location• Monostotic or polystotic (more common) forms.

It is more common in the axial skeleton • with the most common sites being • pelvis, skull & spine.

Proximal long bones are also frequently affected • with the most common among them proximal femur.

Paget disease of long bones begins in the subchondral region of end & advances to the other end.

Hot phase

• Initial phase of increased osteoclastic activity that affects both the cortex and cancellous bone.

Radiological manifestations• Flat bones:

osteoporosis circumscripta.

• There is no surrounding sclerosis (as there is no osteoblastic activity in this phase)

• Long bone:

• candle flame or blade of grass appearance.

Advancing wedge

Intermediate phase(mixed phase)

• Bone destruction accompanied by new bone formation.

Radiological manifestations • Pelvis:Cortical thickening and sclerosis of the ilio-

pectineal and ischio-pubic lines, resulting in obliteration of the tear drop.

• Vertebrae:

Picture frame appearance Cystic spongiosa

Cortical thickening. Coarse trabecular pattern.

• Long bones:

• Cortical thickening.

• Coarse trabecular pattern.

Cold phase

• Disorganized new bone formation

• Skull:

• Cotton wool appearance

• Pelvis:

• Spine:

• Ivory vertebra

• Long bones:

Bone scan• Typically demonstrates marked increased

uptake of radiotracer in all phases

Active phase Mixed phase Inactive phase

The fatty bone marrow is replaced by fibrovascular granulation tissue giving speckled appearance.

Yellow marrow fat signal intensity is maintained or even more bright as the marrow space of pagetic bone actually has more fat than found in the uninvolved bone,

The fatty bone marrow is replaced by increased medullary bone formation

T1 Low signal Bright signal Low signal.

T2 Bright signal.

(more obvious on STIR)

Bright signal Low signal

Contrast enhanced MRI

• Intracortical and speckled intramedullary enhancement due to increased blood flow.

+C