Along with osteoporosis, this is a common degenerative bone disease
 

Epidemiology and Aetiology

This is the second most common bone disorder (after osteoporosis), and affects >5% of the over 55’s in the UK. The prevalence varies between countries and races. The UK has the highest incidence. It is rare in Scandinavia, China and Japan.
  • Increased incidence in Pet Owners
  • Genetic susceptibility
  • Essentially unknown aetiology; environmental factors in a predisposed individual (possibly viral infection is the environmental factor)
  • Incidence increases with age
    • Rare under 50
  • Slight male predominance

Clinical features

  • Chronic progressive disease
  • Often asymptomatic, and discovered incidentally with a raised ALP in the blood, or discovered incidentally on x-ray
  • Only 15-30% of cases have symptoms
  • Bone pain! – the most common symptom
  • May affect bones anywhere in the skeleton, but common sites include; pelvis, lumbar spine, femur, thoracic spine, sacrum, skull, tibia, humerus
  • Usually only affects one site! – it is not ‘systemic’ like osteoporosis, and does not spread to other sites.
  • Osteoarthritis
  • Fractures – bones are prone to fracture because they become more brittle
  • Deafness / Headaches occurs in some patients due to compression of the vestibulocochlear nerve, when the skull is affected
  • Osteosarcomaused to be more common, now only affects 1% of patients.

Pathology

  • Increased number of osteoclasts. Osteoclasts also often larger. The osteoblasts are normal, but are often over active, due to increased factors released by osteoclasts.
  • Essentially, an accelerated rate of bone turnover – with subsequent rapid new bone formation – and this new bone does not have a normal bone matrix – the matrix is disorganised
  • The bones increase in size, but become more brittle, and thus more prone to fracture.

Investigations

Blood tests

  • Raised ALP – ALP can be an indicator of osteoblastic activity
  • Also check γ-GT – to rule out a liver cause!
  • Serum calcium and phosphates will be normal

X-ray

  • Widening of the cortical region – i.e. the hollow cortex at the centre of the bone (where marrow is produced) is wider
  • Mixed areas of sclerosis and lysis – on the x-ray will look like lots of opaque dark splodges in the bone
  • Bone deformities
    • Bone bends anteriorly in the tibia
    • Bone bends laterally in the femur
  • May also show what appears to be localised osteoporosis in areas of very high osteoclast activity – called osteoporosis circumscripta – this is particularly apparent in the skull

Bone scan

Increased isotope uptake in affected bones

Urine

May contain collagen due to very high bone resorption

Treatment

Knowing who and when to treat is the biggest problem. It is essentially based on symptoms severity. Reasons to treat include:
  • Severe pain
  • Nerve compression from expanding bone
  • Fractures
Other management options include:
  • Orthoses – braces, usually plastic that support and protect a bone
  • Analgesia
  • Education
  • Treat the complications – e.g. joint replacement
  • Bisphosphonates
  • These are the ‘mainstay’ of treatment. They inhibit osteoclast activity, and cause osteoclast apoptosis. they damage the cytoskeleton of the osteoclast, so the cell is then unable to bind to bone, and to perform its bone resorption duties.
  • Are often able to induce disease remission. Typical regimen will last 2 months.

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