Fibrous dysplasia is a benign condition, presumably developmental, characterized by the presence of expanding intramedullary fibro-osseous tissue in one or multiple bones.
The incidence is not known, but it is not an uncommon condition.
The exact cause is not known and it is not believed to be hereditary.
A developmental anomaly of bone formation caused by a missense mutation in exon 8 of the GNAS gene (chromosome 20q13.1-13.3). This results in constitutive activation of the adenyl cyclase signaling pathway and synthesis of cyclic adenosine monophosphate (cAMP).
There are three types of fibrous dysplasia.
Monostotic fibrous dysplasia
Polyostotic fibrous dysplasia
Polyostotic fibrous dysplasia with endocrine abnormalities. It is associated with McCune-Albright Syndrome and Mazabraud’s syndrome.
Fibrous dysplasia is more frequent in girls than in boys.
Most lesions probably present in early childhood, however, they usually do not become evident before late childhood to adolescence.
The clinical features are mild in monostotic fibrous dysplasia. It includes mild pain and limp if the neck of the femur is involved.
Sometimes localized swelling is seen in the subcutaneous bone-like mandible, skull or tibia.
In polyostotic form, usually present with severe pain, swelling, deformity, and limb length discrepancy.
The spinal lesion may produce scoliosis.
The most common non-skeletal manifestation includes abnormal cutaneous pigmentation / Café-au-lait spot with serrated borders (Coast of Maine).
Plain radiographs of the affected bone will demonstrate the typical ground glass appearance of the lesion with the eccentric, smooth bordered expansion of the bone with cortical thinning.
Angular deformity of the proximal femur, i.e. Shepherd Crock deformity due to repetitive microfractures is evident.
A bone scan will help classify the lesion and shows an increased uptake throughout the lesion.
Non-surgical treatment is indicated for those with bone pain and when the lesion cannot be improved through surgical intervention.
Bisphosphonates are beneficial in controlling the pain and improving the quality of life.
Surgical treatment is indicated when there is a fracture or there is a painful deformity. Surgical treatment includes –
Curettage and bone grafting
Curettage, intramedullary stabilization, and bone grafting
Curettage, bone graft substitute, stabilization, and intralesional bisphosphonates
Deformity correction and stabilization
Normal medullary bone is replaced by variable amounts of fibrous/osseous tissues.
Overall prognosis – Good
Worst outcomes – Higher local recurrence, younger patients with polyostotic dysplasia
Malignant transformation – Rare