Fibrous dysplasia is an uncommon benign bone tumor like disorder affecting age group between 5 – 30 years. It is a tumor like proliferation of fibro-osseous tissue. They can appear in any bone in the body, more commonly the diaphysis of femur, tibia, humerus, pelvis ribs and craniofacial bones.
What is cause of fibrous dysplasia?
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 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 such as McCune Albright syndrome (Polyostotic fibrous dysplasia, precocious puberty and cafe au lait spots), Mazabraud’s syndrome (fibrous dysplasia and soft tissue tumors) and 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. This when unrecognized or untreated can lead to fatigue fracture or even frank pathological fracture and lead to disability and further complications. 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 above can also be a presenting feature.
Plain radiographs show a characteristic “Ground Glass” appearance of the involved bone. Deformities of long bones, Micro-fractures, Fatigue fractures or Frank Pathological fractures can also be noticed. Bone scan is performed to assess the extent of the disease, especially in polyostotic variety. CT scan is performed to visualize the skeletal architecture of lesion. MRI scan is performed if any other diagnosis is suspected as soft tissue involvement is extremely rare in fibrous dysplasia.
What is 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 (polyostotic > monostotic) is extremely rare (0.4 – 4 %), into osteosarcoma. 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. 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. Any progression in size or characteristics of lesion 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 also 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.
Progressive pain, Limp (assistance to walk), Deformity, Micro-fracture, Fatigue fracture and Frank Pathological fracture are acceptable indications for surgical treatment. Sites more prone for surgical treatment are proximal femur, femur diaphysis and humerus. Extended Curettage and bone graft or with substitutes is performed for contained lesions. If there is a Deformity, an ‘Osteotomy’ (controlled planned fracture) is performed and the bone is fixed with either plate or nail. Procedures to correct deformity are postponed until reaching maturity so as to prevent progression of the same. Micro-Fracture, fatigue fracture may require fixation alone of involved bone. Pathological fracture is an emergency indication for surgical fixation, routinely performed with plate or nail. Combined medical and surgical treatment is employed in many individuals and has shown promising results.