Abnormal and anarchic resorption and deposition, resulting in distortion and weakening of the affected bones

Epidemiology: M > F, patients over 50 years, Max > Mand (2:1)

Etiology:

• Slow paramyxovirus infection
• Vascular disorder
• AD

Pathology:

• Fast, irregular, exaggerated bone remodelling
• Thick bones without localized swelling
• Early phase – resorption
• Late stage – sclerosis
• Patchy appearance due to areas of resorption and sclerosis adjacent to each other

Clinical:

• Simian stance due to weakening of weight bearing bones,
• Lion-like facial deformity (bilat symmetrical bone enlargement)
• Pain on involved bones
• Hypercementosis
• Neurological symptoms due to narrowing of foramina:
  − Headache
  − Vertigo
  − Visual disturbance
  − Auditory disturbance

Complication: (0.9 – 13%): progression to osteosarcoma

Histology:

• Initial osteolytic – osteoclastic bone resorption
• Mixed osteolytic/osteoblastic stage -mosaic pattern of reversal lines (osteoid seams)
• Quiescent osteosclerotic stage – dense bone with remnants of mosaic patterns

X-ray:

• “Cotton wool” appearance of confluent radio-opacities
• Thickening of bone
• Irregular areas of sclerosis and resorption
• Loss of normal trabeculation

Lab:

• ↑alkaline phosphatase
• Normal calcium and phosphorus levels
• ↑ urinary hydroxyproline

Management: Seldom fatal

• Surgical debulking + calcitonin (PTH antagonist) + sodium phosphatase (retards bone resorption)

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