Fibrous Dysplasia: Definition, Symptoms, Causes, Diagnosis and Treatment

It is a disorder where the bone and marrow are replaced with fibrous tissue, which results in the formation of a bone that is weak and prone to expansion.

As a result, most complications are the result of a fracture, deformity, functional deterioration and pain.

The disease occurs along a broad clinical spectrum ranging from asymptomatic incidental lesions to a serious disabling disease.

The disease can affect a bone (monostotic) or multiple (polyostotic), and can occur in isolation or in combination with skin macules and hyperfunctioning endocrinopathies , called McCune-Albright syndrome.

More rarely, fibrous dysplasia may be associated with intramuscular myxomas, called Mazabraud syndrome. Fibrous dysplasia is very rare and a cure is not known. Fibrous dysplasia is not a form of cancer.

Presentation

Fibrous dysplasia is a mosaic disease that can involve any part or combination of the craniofacial, axillary and / or appendicular skeleton.

The type and severity of complications, therefore, depend on the location and extent of the affected skeleton.

The clinical spectrum is very broad and ranges from an isolated and asymptomatic monostotic lesion discovered incidentally to a severe disabling disease that affects practically the entire skeleton and leads to loss of vision, hearing and / or mobility.

Individual bone lesions usually manifest during the first years of life and expand during childhood.

The vast majority of clinically significant bone lesions are detectable at the age of 10 years, with few new and almost nil clinically significant bone lesions appearing after 15 years.

The total body scan is useful to identify and determine the extent of bone lesions, and should be performed in all patients with suspected fibrous dysplasia.

symptom

Children with fibrous dysplasia in the appendicular skeleton typically present with lameness, pain and / or pathological fractures. Frequent fractures and progressive deformity can cause difficulties with mobility and reduced mobility.

In the craniofacial skeleton, fibrous dysplasia may present as a “lump” or painless facial asymmetry. The expansion of craniofacial injuries can lead to a progressive facial deformity.

In rare cases, patients may develop loss of vision and / or hearing due to the involvement of optic nerves and / or auditory ducts, which is more common in patients with excess growth hormone associated with McCune-Albright syndrome.

Fibrous dysplasia usually affects the spine and can cause scoliosis, which can rarely be serious. The untreated progressive scoliosis is one of the few features of fibrous dysplasia which can lead to early death.

Bone pain is a common complication of fibrous dysplasia. It can occur at any age, but more often it develops during adolescence and progresses to adulthood.

Stromal cells of the bone marrow in fibrous dysplasia produce excess amounts of the fibroblast growth factor of the phosphate-regulating hormone-23 (FGF23), which leads to the loss of phosphate in the urine.

Patients with hypophosphatemia may develop rickets / osteomalacia, increased fractures and bone pain.

Causes

Fibrous dysplasia is a mosaic disease resulting from post-zygotic activation mutations of the GNAS locus protein at 20q13.2-q13.3, which encodes the α subunit of the Gs protein receptor coupled to G.

In bone, the constitutive signaling of Gsα results in damaged differentiation and proliferation of stromal cells of the bone marrow. The proliferation of these cells causes the replacement of normal bone and marrow with fibrous tissue.

Bone trabeculae are abnormally thin and irregular, and often resemble Chinese characters (bone spicules in the biopsy).

Fibrous dysplasia is not hereditary, and there has never been a case of transmission from parents to children.

Diagnosis

X-rays:  can be used to determine how extensively your bones are affected.

X-ray : This test uses radioactive markers, which are injected into the bloodstream. The damaged parts of your bones occupy more of the tracers, which appear brighter in the scan.

Biopsy : This test uses a hollow needle to remove a small portion of the affected bone for analysis in the laboratory.

Treatment

The treatment in fibrous dysplasia is mainly palliative, and focuses on the management of fractures and the prevention of deformity.

There are no drugs capable of altering the course of the disease. Intravenous bisphosphonates may be useful for the treatment of bone pain, but there is no clear evidence that they strengthen bone lesions or prevent fractures.

Surgical techniques that are effective in other disorders, such as bone grafting, curettage, and plates and screws, are often ineffective in fibrous dysplasia and should be avoided.

The intramedullary rods are generally preferred for the treatment of fractures and deformities in the lower extremities. Progressive scoliosis can usually be treated with standard instrumentation and fusion techniques.

Surgical treatment in the craniofacial skeleton is complicated by the new growth of postoperative fibrous dysplasia, and should focus on the correction of functional deformities.

Prophylactic decompression of the optic nerve increases the risk of vision loss and is contraindicated.

The management of endocrinopathies is a critical component of treatment in fibrous dysplasia. All patients with fibrous dysplasia should be evaluated and treated for endocrine diseases associated with McCune-Albright syndrome.

In particular, excess untreated growth hormone can worsen craniofacial fibrous dysplasia and increase the risk of blindness. Untreated hypophosphatemia increases bone pain and the risk of fractures.