Paget's disease of bone

Paget’s disease of the bone is a chronic bone disorder characterised by excessive abnormal bone remodelling. It is relatively common and can affect upto 4% of individuals over 40 and up to 11% over the age of 80 ¹ .

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)

These stages correspond to scintigraphic stages: hot; intermediate; and cold. The aetiology is not entirely known, however viral infection in association with genetic susceptibility has been postulated.

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

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

Radiographic features

Plain film

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,

Bone scintigraphy

Extremely sensitive but not specific. Demonstrates marked increased uptake in all phases of disease ¹ .

Other Paget's disease related signs

• Tam O'Shanter sign
• blade of grass sign
• osteoporosis circumscripta
• jigsaw pattern bone or mosaic pattern bone
• picture frame vertebra
• cotton wool appearance of bone
• banana fracture

Complications

• osseous weakening resulting in deformity and fractures
• arthritis
• neural compression
  • deafness is the most common complication
  • cranial nerve paresis may occur
  • basilar invagination may occur in advanced cases with hydrocephalus or brainstem compression
• secondary development of osteosarcoma (one percent of cases), which is often highly resistant to treatment
• high output congestive cardiac failure
• hyperparathyroidism (approximately 10 %)

Differential diagnoses

• hyperostosis frontalis interna : thickening of the internal table of the frontal bone
• fibrous dysplasia 

Etymology

First described by Sir James Paget in 1877.