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Fibrous Dysplasia: Causes, Symptoms and Treatment

Fibrous dysplasia is a rare bone disorder in which normal bone tissue is replaced by fibrous connective tissue. It can affect one or multiple bones and may cause pain, deformity, and fractures.

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Things worth knowing about "Fibrous Dysplasia"

Fibrous dysplasia is a rare bone disorder in which normal bone tissue is replaced by fibrous connective tissue. It can affect one or multiple bones and may cause pain, deformity, and fractures.

What is Fibrous Dysplasia?

Fibrous dysplasia is a rare, non-hereditary skeletal disorder in which normal bone tissue is progressively replaced by abnormal fibrous connective tissue. This replacement weakens the affected bone, making it prone to deformity and fracture. The condition arises from a spontaneous, somatic mutation in the GNAS1 gene, which encodes the signaling protein Gαs. This mutation prevents immature bone-forming cells from developing into healthy, mature bone tissue.

Fibrous dysplasia can be classified as monostotic (affecting a single bone) or polyostotic (affecting multiple bones). In rare cases, it occurs as part of McCune-Albright syndrome, which additionally involves characteristic skin pigmentation (café-au-lait spots) and hormonal disturbances.

Causes

Fibrous dysplasia is caused by an acquired, somatic mutation in the GNAS1 gene located on chromosome 20q13. Because this mutation occurs in body cells rather than reproductive cells, it is not inherited and cannot be passed on to children. The mutation occurs randomly during early embryonic development, and the extent of the disease depends on how early and in how many cells the mutation arises.

Monostotic form: Mutation affects only a small number of cells; only one bone is involved (approximately 70-80% of cases)
Polyostotic form: Earlier mutation affects more cells and multiple bones (approximately 20-30% of cases)
McCune-Albright syndrome: Additional involvement of skin and endocrine glands

Symptoms

The symptoms of fibrous dysplasia vary depending on which bones are affected and the severity of the lesions. Common manifestations include:

Bone pain, particularly with weight-bearing activity
Bone deformities (e.g., bowing of the femur, known as a "shepherd's crook" deformity)
Pathological fractures (fractures occurring with minimal trauma)
Leg length discrepancy when the lower limbs are involved
Facial asymmetry when the skull base or facial bones are affected
Visual or hearing disturbances when bones near the skull are involved

In many patients, especially those with the monostotic form, fibrous dysplasia may be entirely asymptomatic and discovered incidentally during imaging performed for another reason.

Diagnosis

The diagnosis of fibrous dysplasia is established through a combination of clinical evaluation, imaging studies, and in some cases a bone biopsy.

X-ray: Typically reveals a characteristic "ground-glass" appearance and structural changes within the affected bone
Computed Tomography (CT): Provides detailed visualization of bone lesions
Magnetic Resonance Imaging (MRI): Used to assess soft tissue involvement
Bone scintigraphy: Identifies all affected skeletal regions throughout the body
Biopsy: Histological examination of bone tissue to confirm the diagnosis
Genetic testing: Detection of the GNAS1 mutation is possible but not always required

Treatment

Currently, there is no curative treatment for fibrous dysplasia. Management focuses on relieving pain, preventing fractures, and correcting deformities.

Medical Treatment

Bisphosphonates (e.g., pamidronate, zoledronic acid) are the primary pharmacological option. They work by inhibiting bone resorption and have been shown to reduce pain and improve bone density in affected areas. They are considered the first-line treatment for symptomatic patients.

Surgical Treatment

Surgery is indicated for severe deformities, pathological fractures, or impending complications. Procedures may include:

Internal fixation using intramedullary nails, plates, or screws (osteosynthesis)
Corrective osteotomy to address axial malalignment
Bone grafting in selected cases

Additional Management

Physiotherapy to strengthen surrounding muscles and maintain mobility
Regular orthopedic follow-up and imaging surveillance
In McCune-Albright syndrome: treatment of associated endocrine disorders

Prognosis

Fibrous dysplasia is generally a lifelong condition. Lesions may progress during periods of skeletal growth and often stabilize once skeletal maturity is reached. The prognosis depends largely on the extent and location of the disease. Malignant transformation is possible but extremely rare, occurring in fewer than 1% of cases.

References

Riminucci M, Robey PG, Bianco P. - Fibrous Dysplasia. In: Rosen CJ (ed.), Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 8th edition. Wiley-Blackwell, 2013.
Boyce AM, Collins MT. - Fibrous Dysplasia/McCune-Albright Syndrome. GeneReviews, NCBI Bookshelf, 2020. URL: https://www.ncbi.nlm.nih.gov/books/NBK274564/
Leet AI, Collins MT. - Current approach to fibrous dysplasia of bone and McCune-Albright syndrome. Journal of Children's Orthopaedics, 2007; 1(1): 3-17.

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