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Fibrous dysplasia is a chronic condition of the skeleton where a portion of a bone develops abnormally.
The condition begins before birth. It is caused by a gene mutation that affects the cells that produce bone. Although the abnormal bone forms before birth, its presence is often not discovered until childhood, adolescence, or even adulthood.
Fibrous dysplasia accounts for approximately 7% of all benign bone tumors. Any bone may be affected. The most common bones involved are the thighbone, shinbone, ribs, skull, upper arm bone, and pelvis.
Usually, only one bone is involved (monostotic fibrous dysplasia). Less often, multiple bones are involved (polyostotic fibrous dysplasia). The polyostotic form is generally more severe and is discovered earlier. This form can involve as few as two bones in the same limb or multiple bones throughout the skeleton.
The same abnormality that occurs in the bone cells of fibrous dysplasia may also occur in the cells of some of the body's glands. This can lead to hormonal abnormalities. This is rare and generally only happens with severe forms of polyostotic fibrous dysplasia. McCune-Albright syndrome is a condition where polyostotic fibrous dysplasia occurs with pigmented skin lesions ("cafe au lait" spots) and hormonal abnormalities.
The cause of the gene mutation is not known. It is not inherited or passed on to the children of affected patients. No dietary or environmental cause is known. It occurs equally among males and females of all races.
As the abnormally formed fibrous tissue grows and expands, the involved area of bone becomes weaker. The weakened area of bone can become painful. Pain is more likely to occur in the weightbearing leg and pelvis bones. This type of pain generally begins as a dull ache that is made worse with activity and lessened with rest. It can progressively increase with time.
Severe deformity can lead to loss of vision or hearing when facial bones are involved. When the leg and pelvis bones are severely deformed, arthritis may develop in nearby joints.
Young patients with hormonal abnormalities may develop early puberty. This problem is more common in girls than boys. This is usually caused by overactivity of the ovaries. Overactivity may also occur in other glands of the body, including:
- the thyroid gland (causing anxiety, loss of weight, and abnormal sweating)
- the adrenal glands (causing weight gain, diabetes)
- the pituitary gland (causing milk production in women, gigantism, acromegaly)
- the parathyroid glands (causing high levels of calcium in the blood)
Pigmented skin lesions are often seen in patients with fibrous dysplasia and hormonal abnormalities.
The elevated hormone levels normally associated with pregnancy may speed up the growth of fibrous dysplasia lesions, causing increased pain.
Warning signs that an area of fibrous dysplasia may have become cancerous include increasing pain, particularly pain that wakes you up at night or does not go away with rest. The presence of a mass should always be investigated.
A doctor can usually diagnose fibrous dysplasia based in part on x-rays. The x-rays may show:
- An abnormal area of bone that typically has an appearance similar to that of ground glass
- Frequently, expansion of the involved area of bone
- Deformity of the bone that is usually seen as bowingFibrous dysplasia in the shinbone with bowing. Left, Side view X-ray shows the area of dysplasia. Center, Magnetic resonance image (MRI) of the same area, showing the dysplasia. Right, Cross-sectional MRI of the area, showing the dysplasia.
If a fracture is present, it will generally be seen on x-ray and/or MRI. A computed tomography (CT) scan may help the doctor to see fractures and determine the weakness of the bone.
Areas of fibrous dysplasia can rarely become cancerous. This occurs in less than one half of 1% of patients. With McCune-Albright syndrome, this may occur in 4% of patients. If cancer occurs, the x-ray will generally show areas of bone destruction. MRI may show an associated mass in the surrounding tissues.
Fibrous dysplasia is a chronic disorder. It is often progressive. Although lesions may stabilize and stop growing, they do not disappear. Individual lesions may progress more rapidly in the polyostotic form and in growing children.
Observation. Areas of fibrous dysplasia that are not symptomatic may be observed with periodic x-rays and not treated if they are not progressing. Braces may occasionally be used to prevent fracture, but they have not been effective in preventing deformity.
Medications. Bisphosphonates are medications that decrease the activity of cells that dissolve bone. They have recently become available in easy to take oral forms. These medications have not been used extensively in the treatment of fibrous dysplasia, but early studies have demonstrated effective relief of the pain associated with fibrous dysplasia.
Surgical treatment is often necessary. The following findings are associated with the need for surgery.
- Symptomatic lesions that have not responded to nonsurgical treatment
- Displaced fractures (when the bone breaks into two or more separate pieces)
- Hairline cracks that do not heal with casting or bracing
- Progressive deformity
- Presence of cancer
- As a means to prevent large lesions from causing a fracture
Additionally, scooping out (curettage) of the fibrous dysplasia is generally performed along with bone grafting. Over time, the bone graft placed in the defect often is absorbed and replaced with more fibrous dysplasia.
The explosion of genetic research may lead to a better understanding of the exact mutation involved in fibrous dysplasia. That may lead to more effective nonsurgical treatments.
Newer generations of medications, like the bisphosphonates, have made them easier to take with fewer side effects. More experience with these medications may allow more effective treatment.
The American Academy of Orthopaedic Surgeons
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