Fibrous Dysplasia
Background
Fibrous dysplasia is a rare bone disorder in which scar tissue develops in place of normal bone tissue, thereby weakening the bone. In more severe cases this results in deformity and intense pain. Any bone in the body can be affected. The most common bones affected by this disease are the skull and facial bones, thighbone, shinbone, pelvic bones, ribs, and upper arm bone. In the majority of patients, only one bone is affected, but approximately 20-30% of cases are polyostotic, involving multiple bones. Fibrous dysplasia is established early in life, and though it does not spread beyond the original scope of affected bones, it is irreversible. The polyostotic form usually becomes apparent before age 10, whereas detection of the monostotic form (only one bone is affected) depends upon what bone is affected. In cases where there are no symptoms, it may not be discovered until later in life, and then only incidentally.
Causes/ Risk factors
Fibrous dysplasia has been linked to an abnormality in a gene that produces bone. The causes of this mutation are unknown. It is not inheritable.
Symptoms
In many cases of monostotic fibrous dysplasia there are no symptoms. When symptoms are present, they depend upon the bone affected. If a leg bone is affected, for example, a child may have difficulty walking, or the bone may fracture easily. If the skull or facial bones are affected, deformities of the head or face may be present. Bone pain and swelling in the affected area is the most common symptom.
Additionally, light brown birth marks (referred to as café-au-lait spots) may accompany fibrous dysplasia, along with endocrine dysfunctions such as premature puberty, hyperthyroidism and excessive production of growth hormone. These are signals of a condition called McCune-Albright syndrome, of which polyostotic fibrous dysplasia is one manifestation.
Diagnosis
Images provided by x-rays, MRI, and/or CT scans can reveal the presence of abnormal tissue in bones and the extent to which bones are affected. A bone scan may also be ordered. In this test radioactive tracers are injected into the body and taken up by the bones. A specialized camera captures the radiation they emit, producing a picture of the skeleton. In cases of polyostotic fibrous dysplasia, blood tests to assess endocrine function may also be required.
Biopsy is used in cases where there is suspicion of cancer. In severe cases of fibrous dysplasia, the bone lesions can become malignant. However, this is a rare occurrence.
Treatment
For mild cases with no symptoms, treatment may consist of long term observation by a physician. Medical therapy is effective for most upper-extremity lesions. For more problematic cases involving chronic pain, fractures or deformity, surgery may be necessary.
Medications: The medications used in the treatment of fibrous dysplasia are the same medications used in the treatment of osteoporosis. They act to inhibit bone breakdown, preserve existing bone, and increase bone density. Medications are also prescribed for pain management, as well as to correct endocrine dysfunction.
Surgery: Surgical treatment for fibrous dysplasia involves removal of the affected bone, followed by a bone graft from another part of the body. Stabilizing agents such as metal plates, rods and screws may also be inserted during surgery. The surgical approach depends upon the location of the affected bones.
Patients with fibrous dysplasia require long term follow up to monitor the disease. The re-growth of fibrous tissue in the affected bone and/or absorption of the graft by fibrous tissue has been reported in about 20% of cases following surgery. However, the lesions tend to become stable as bones mature.
Particularly in cases in which the fibrous dysplasia causes cranial nerve deficits as in the case of vision loss, surgery for optic nerve decompression is imperative.
Fibrous dysplasia of the skull base can be directly approached through expanded endonasal approach (EEA). This state-of-the-art, minimally invasive surgical procedure uses the nose as a natural corridor to reach these lesions. There are no incisions in the skin of the face or head. The optic nerves can be directly decompressed by the removal of the deformed optic canal through the nose.
Prevention
There are currently no guidelines for preventing fibrous dysplasia. However, early intervention may help to prevent progression of the disease.