Fibrous Dysplasia

Fibrous dysplasia is an uncommon benign bone tumor-like disorder affecting age groups between 5 – 30 years.

It is a tumor-like proliferation of fibro-osseous tissue.

Location

  • They can appear in any bone in the body
  • More common is descending order, diaphysis of femur, tibia, humerus, pelvis ribs and craniofacial bones.

Etiology

  • Etiology of fibrous dysplasia is linked to G-alpha gene which is located in Chromosome 20.
  • This is also found in a form of syndromic fibrous dysplasia-McCune Albright syndrome.
  • It appears to be a tumor-like proliferation of fibrous and osseous tissue in the form of immature woven bone which can slowly expand the original structure of the bone.
  • It is also suspected to be due to failure of the bone not remodeling due to the mechanical stress.
  • This can slowly, over years can lead to pain, deformity and even fractures (nearly 50 % in monostotic variety).

What are types of fibrous dysplasia?

Fibrous dysplasia can affect a single bone (Monostotic) or multiple bones (Polyostotic).

  • Monostotic component is a milder version, commonly asymptomatic and an incidental finding on plain radiographs.

Rarely, monostotic variety can present with pain or pathological fracture.

  • Polyostotic is usually a component of syndromes associated with fibrous dysplasia
    • McCune Albright syndrome (Polyostotic fibrous dysplasia, precocious puberty and cafe au lait spots)
    • Mazabraud’s syndrome (fibrous dysplasia and soft tissue tumors)
    • Cushing’s disease.

How is fibrous dysplasia identified?

Majority of monostotic lesions are asymptomatic and incidentally found.

  • Localized bone pain should be investigated and is caused by ‘Micro-Fractures’ in the lesion.
  • An unrecognized or untreated lesion can lead to fatigue fracture or even frank pathological fracture and lead to disability.
  • Deformity of monostotic bone is noticed depending on age, duration and extent of lesion.
  • Growing children can have a bent spine if any spine element is affected.

Any component of the syndromes discussed prior can also be a presenting feature.

Imaging

  • Plain radiographs show a well defined lesion with characteristic “Ground Glass” appearance of the involved bone.

A Skeletal survey is done when other bone involvement is suspected.

  • Deformities of long bones, Micro-fractures, Fatigue fractures or Frank Pathological fractures can also be noticed.
  • Bone scan is performed to assess the Activity and Extent of the disease, especially in polyostotic variety.
  • CT scan is performed to visualize the skeletal architecture of lesions.
  • MRI scan is performed if any other diagnosis is suspected as soft tissue involvement is extremely rare in fibrous dysplasia.

What is the course of fibrous dysplasia?

  • Natural history of monostotic fibrous dysplasia is to mature by adulthood.
  • An occurrence of events as described above needs attention, preferably a combined medical and surgical approach.
  • Malignant transformation of fibrous dysplasia into osteosarcoma or pleomorphic sarcoma (polyostotic > monostotic) is extremely rare (0.4 – 4 %).
  • Individuals with fractures in fibrous dysplasia have high risk of nonunion, malunion and episodes of refracture.

What are treatment options for fibrous dysplasia?

Many lesions are discovered incidentally and are asymptomatic.

  • Monostotic Fibrous dysplasia can be diagnosed by plain radiographs alone.

So CT, MRI and Bone scan are performed only in doubtful diagnosis.

Consequently Biopsy is performed only in confirming a doubtful diagnosis.

These monostotic lesions can be followed up every 6 months and can be managed conservatively.

If symptomatic (No Micro-fractures) then a trial of Zoledronic acid helps relieve the pain.

Any progression in size or characteristics of lesions or any event may require intervention.

  • Polyostotic component should be addressed in a multidisciplinary mode involving pediatrics, endocrine, genetics and gynecologist.

Pain is currently successfully treated by Bisphosphonates (Oral Alendronate daily, Intravenous Pamidronate every 6 months or Zoledronic acid once a year).

There is radiologically visible strengthening of involved bone.

This treatment is not continued beyond 2 years due to fear of complications and side effects of bisphosphonates over long term usage.

Indications for Surgery

  • Progressive pain
  • Limp (assistance to walk)
  • Deformity
  • Micro-fracture
  • Fatigue fracture
  • Frank Pathological fracture.

Sites more prone for surgical treatment are proximal femur, femur diaphysis and humerus.

Mechanical Stabilisation is the Goal of Treatment.

Indications are

  • Micro-Fracture
  • Impending Fracture
  • Pathological Fracture
  • Deformity Correction
  • Extended Curettage and bone graft or with substitutes is performed for contained lesions, But Graft resorption and failure is high when done alone.

Procedures to correct deformity are postponed until reaching maturity so as to prevent progression of the same.

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