Fibrous dysplasia is a rare disorder of the bone in which abnormal, fibrous tissue (tumor) develops in the place of bone. The disease may occur in one of three categories, depending on how many bones are affected, and if there are other symptoms: monostitic, polyostotic, or the McCune-Albright syndrome. In patients with monostotic disease, there is only one area of bony involvement. Around 70% of patients have monostotic disease. In 20-30% of patients, the disease is polyostitic, meaning multiple bony sites are involved. Approximately 3% affected patients have the McCune-Albright syndrome. Patients with the McCune-Albright syndrome have the triad of polyostotic fibrous dysplasia, precocious puberty (early puberty), and areas of abnormal skin pigmentation called café-au-lait spots.
What causes fibrous dysplasia?
Fibrous dysplasia is caused by a mutation in a gene coding for a protein called G-protein. This type of protein functions to transmit signals, from hormones, through cells, to create specific productivity by the cell. The mutation in fibrous dysplasia causes the signaling pathway to remain in an activated state. The net effect, as in which body parts body parts are affected, depends on whether the disease in monostitic, polyostotic, or the McCune-Albright syndrome.
It is thought that fibrous dysplasia is the result of a mutation that occurs some time in embryogenesis. The disease is not known to be heritable; parents have not been known to pass the disease on to children. It is thought that when, in embryogenesis, the disease occurs results in the manifestation. In other words, when the mutation occurs later in embryologic development, only one part of the skeleton is affected. A mutation which occurs earlier in development, in which each mutation may affect more body parts, may lead to polyostotic disease or the McCune-Albright syndrome.
What is affected in fibrous dysplasia?
Fibrous dysplasia may involve nearly any part of the skeleton. In the extremities, the lesions may present as pain from pathologic fractures, or fractures in the areas of abnormal bone weakened by the disease. In the craniofacial region, which is involved in 25% of patients with monostotic fibrous and 50% of patients with polyostotic fibrous dysplasia, the disease typically presents as a painless bony mass, or may be found incidentally after CT scanning for another reason. The effects of the abnormal bone growth depend on where in the facial skeleton the growth occurs. In the maxilla (upper jaw) or mandible (lower jaw,) growth may affect occlusion, or the way teeth fit together when biting. Patients with sphenoid (a bone at the base of the skull) may be at risk for blindness if the lesion compresses the optic nerve. Lesions in the orbit (eye socket) may lead to proptosis (bulging of the eye), orbital dystopia (asymmetry in the location of the eye socket on the face), double vision, or other visual disturbances. Rarely, particularly in polyostotic disease or the McCune-Albright syndrome, the bony lesions can undergo malignant degeneration, or become cancerous.
How is fibrous dysplasia diagnosed?
Diagnosis of fibrous dysplasia is typically made based on patient history, physical examination, laboratory examinations, and imaging. The lesions have a typical appearance on CT scans and x-rays. Occasionally, particularly when the lesions involve the craniofacial skeleton, biopsy is warranted to confirm the diagnosis.
How is fibrous dysplasia treated?
The treatment of fibrous dysplasia depends on the locations of the lesions, and whether they are symptomatic. Patients with the McCune-Albright syndrome are referred to an endocrinologist for management of endocrine abnormalities. In the extremities, treatment by an orthopedic surgeon may be warranted in the event of pain or pathologic fracture. This may include curettage (scraping out the diseased bone), bone grafting, and/or fixation with plates and screws. Medications called bisphosphonates have been found to decrease pain in patients with fibrous dysplasia.
In the craniofacial skeleton, surgery is indicated in lesions that become symptomatic, altering the facial form or function. In many cases, the bone lesions can be observed over time, often with serial imaging in the form of CT scans. If they do cause noticeable deformity, options for treatment include recontouring the area of diseased bone by using a burr, or resection of the diseased area and replacement with bone grafts of free flaps. The decision over which procedure is appropriate depends on the location of the lesion and how aggressively it is growing. Recontouring is a less invasive procedure, but there is a risk of the deformity recurring.
If you would like more information about fibrous dysplasia, please contact the Craniofacial Team of Texas by calling 512-377-1142 or toll free 877-612-7069 to schedule an appointment or complete an online appointment request.