Paget disease of bone

Paget disease of the bone is a common, chronic bone disorder characterised by excessive abnormal bone remodelling. It frequently affects the pelvis, spine, skull and proximal long bones and has characteristic radiographic features.

Epidemiology

It is relatively common and can affect up to 4% of individuals over 40 and up to 11% over the age of 80 1. There may be a slight male predilection. Incidence can be considerably higher in the United Kingdom than in other countries 8. It is also common in Australia, New Zealand, Western Europe, and the United States.

Clinical presentation

The majority (approximately three-quarters) of patients are asymptomatic at the time of diagnosis. Presenting symptoms include:

  • localised pain and tenderness
  • increased focal temperature due to hyperaemia (due to hypervascularity)
  • increased bone size: historically changing hat size was a giveaway
  • bowing deformities
  • kyphosis of the spine
  • decreased the range of motion
  • signs and symptoms relating to complications (see below)

Polyostotic disease is more prevalent than the monostotic type 1. The most frequent sites of involvement are:

  • spine
  • pelvis (often asymmetric)
  • skull
  • proximal long bones

Pathology

The aetiology is not entirely known, but it is a disease of osteoclasts. Viral infection (paramyxovirus) 6 in association with genetic susceptibility has been postulated.

There are three stages classically described (but is part of continuous spectrum)

  • lytic (incipient active): predominated by osteoclastic activity
  • mixed (active): osteoblastic as well as osteoclastic activity
  • sclerotic/blastic (late inactive)
Markers
  • serum alkaline phosphatase (ALP) elevated
  • normal calcium and phosphorous levels
  • urine hydroxyproline increased

Radiographic features

Plain radiograph

The early phase features osteolytic (lucent) region which is later followed by coarsened trabeculae and bony enlargement. Sclerotic changes occur much later in the disease process.

Skull
  • osteoporosis circumscripta: large, well-defined lytic lesion
  • cotton wool appearance: mixed lytic and sclerotic lesions of the skull
  • diploic widening: both inner and outer calvarial tables are involved, with the former usually more extensively affected
  • Tam o'Shanter sign: frontal bone enlargement, with the appearance of the skull falling over the facial bones, like a Tam o' Shanter hat
Spine
  • picture frame sign: Paget disease of the spine frequently manifests with cortical thickening and sclerosis encasing the vertebral margins, which gives rise to this appearance on radiographs in mixed phase disease
  • squaring of vertebrae: on lateral radiographs, flattening of the normal concavity of the anterior margin of the vertebral body also adds to the rectangular appearance
  • vertical trabecular thickening in Paget disease is coarser than the more delicate pattern seen in intraosseous hemangiomas with which it may be confused
Pelvis
  • cortical thickening and sclerosis of the iliopectineal and ischiopubic lines
  • acetabular protrusio
  • enlargement of the pubic rami and ischium

These findings are often asymmetric, and for some reason, are more commonly seen on the right side.

Long bones
  • blade of grass or candle flame sign: begins as a subchondral area of lucency with advancing tip of V-shaped osteolysis, extending towards the diaphysis
    • in rare cases, the disease is isolated to the diaphysis, most commonly in the tibia, rather than subchondral bone, which can cause diagnostic confusion
  • lateral curvature (bowing) of the femur
  • anterior curvature of the tibia
Signs

Paget disease related signs include:

MRI

The overall signal characteristics are variable, likely reflecting the natural course of the disease process in different phases.

Several major patterns of involvement have been described 8

  • dominant signal intensity in pagetic bone similar to that of fat; most common pattern: probably corresponds to the early mixed active phase
  • relatively low T1 and high T2 signal alteration (also referred as a “speckled” appearance); second most common pattern: probably corresponds to granulation tissue, hypervascularity, and oedema seen in active disease
  • low signal intensity on both T1 and T2 images: suggesting the presence of compact bone or fibrous tissue; least common pattern: seen in late blastic inactive phase

Fatty marrow signal is usually preserved in all sequences unless there is a complication 10.

Bone scintigraphy
  • Tc99m-MDP
    • highly sensitive but not specific
    • traditionally has been said to demonstrate marked increased uptake in all phases of the disease, although in the burnt out sclerotic quiescent phase uptake may be normal 1

Treatment and prognosis

Symptomatic patients are treated with bisphosphonates (e.g. Alendronate) aiming to reduce the bone turnover, to promote healing of osteolytic lesions and  improve bone pain. Analgesics and nonhormonal anti-inflammatory drugs are also prescribed for pain management. 

Complications

History and etymology

Sir James Paget first described it in 1877 in a case report of a patient he had observed over some twenty years 5.

The condition was initially named by Paget "osteitis deformans", implying an inflammatory aetiology. The term "osteodystrophica deformans" is now preferred.

Differential diagnosis

For skull lesions consider

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Article Information

rID: 1824
System: Musculoskeletal
Section: Pathology
Synonyms or Alternate Spellings:
  • Paget disease of the bone
  • Paget disease of bone
  • Osteitis deformans
  • Paget disease of the bones
  • Paget disease of bones
  • Paget's disease of bones
  • Paget's disease of the bones
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    Figure 1: histopathology
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    CT Axial
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    Paget disease
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    Paget disease
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    Case 8: with secondary osteosarcoma
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    Case 12: involving sternum
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    Case 13: on MRI
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    Case 18: polyostotic involvement
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    Case 21
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    Case 22: with blade of grass sign
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    Case 23
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    left hip
    Case 24: affecting femur
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    Case 25: right iliac bone
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