Brief overview
- Prognosis: Generally good, course often ends at the end of puberty; even the severe and very rare form McCune-Albright syndrome is treatable
- Causes and risk factors: Non-hereditary mutation of a specific gene (GNAS gene) on chromosome 20, cause not yet researched, usually occurs before, sometimes after birth
- Diagnostics: X-ray, computer tomography, tissue samples and further examinations if several bones are affected.
- Treatment: Depending on severity and location, treatment of symptoms; splinting of affected bones, physiotherapy, surgical removal of bone growths; in the case of McCune-Albright syndrome, treatment of further symptoms; therapy of the causes is not yet possible
What is fibrous dysplasia?
Fibrous dysplasia is due to a genetic defect, but is not hereditary. Both male and female sexes are affected, although forms with several affected bones (polyostotic fibrous dysplasia or Jaffé-Lichtenstein syndrome) seem to occur more often in girls. Children and adolescents between five and 15 years of age are most frequently affected, but adults are less frequently affected.
Fibrous dysplasia: Different manifestations
Doctors distinguish different forms of the disease:
- Monostotic fibrous dysplasia (70 percent): only one bone is affected
- Polyostotic fibrous dysplasia (25 percent): several bones are affected (Jaffé-Lichtenstein syndrome)
- McCune-Albright syndrome (very rare): fibrous dysplasia with “café-au-lait spots” (pigment disorder) and premature sexual maturity
Is fibrous dysplasia curable?
Fibrous dysplasia has a good prognosis. The course varies from case to case. In some patients, the foci increase in size during puberty, so that the affected bones are further distended. As a rule, however, no new foci develop. By adulthood at the latest, fibrous dysplasia usually comes to a halt and the bone is not remodeled any further. Three out of four affected patients are under 30 years of age.
Even the very rare course of McCune-Albright syndrome with many affected bones, premature puberty and a variety of other possible symptoms is basically treatable according to the symptoms. Without therapy, affected individuals may have a reduced life expectancy.
If fibrous dysplasia is treated early, affected individuals have no limitations on their quality of life.
Causes and risk factors
Ultimately, the mutation leads to the spongy inner layer of the bone – known as cancellous bone – not being formed properly. In its place is a soft, non-mineralized, connective tissue-like bone substance (osteoid). The cells divide before they are properly differentiated, which often causes the bone to become downright distended.
How does fibrous dysplasia manifest itself?
Fibrous dysplasia progresses very differently. Therefore, symptoms vary depending on the severity and which bones are affected. While some affected individuals are completely asymptomatic, others present with a variety of symptoms:
- Slightly pulling bone pain
- Strain pain (such as when the femur is affected)
- Difficulty walking, so that some sufferers walk with a limp
- Externally visible “bumps,” curvatures, and other changes in the bones (such as a visibly deformed facial skull)
- Rapid physical development in affected children and adolescents (rapid growth and early puberty)
- Pigmentation disorders, so-called café-au-lait spots
The premature onset of puberty is due to a change in hormone balance. Sometimes fibrous dysplasia occurs together with other hormonal disorders, such as diabetes, Cushing’s disease or hyperthyroidism.
Depending on the region affected, the fibrous growths press on nerves or blood vessels in or on the bones, leading to symptoms such as pain or circulatory problems.
Frequently affected bones
In principle, fibrous dysplasias are possible in all bones, but they are particularly common in the following regions:
- Bones of the skull
- Face, often the jaw
- Ribs
- Upper arm
- Hip
- Thigh
- Shin
Fibrous dysplasia: examinations and diagnosis
The physician may draw blood from the affected person. In the case of fibrous dysplasia, the blood serum shows normal levels of calcium and phosphate, but the level of the enzyme alkaline phosphatase is often elevated. This blood value belongs to a group of enzymes that, among other things, often indicate changes in bone metabolism.
The outer layer of bone (cortical bone) is usually thinner than in a healthy bone. A computed tomography (CT) scan helps the doctor look at the changes even more closely. In this process, the person being examined lies in a special device that produces very precise X-ray images of the body layer by layer in the form of cross-sectional images.
Especially when only a single bone is changed (monostotic fibrous dysplasia), the correct diagnosis by imaging techniques is sometimes difficult, because some other diseases present themselves similarly (such as bone cysts, benign fibrous histiocytoma, hemangioma, chondrosarcoma). In this case, the physician takes a tissue sample from the altered area (biopsy), which is then examined under the microscope.
Treatment
A causal treatment is not possible for fibrous dysplasia. If the femur or tibia is affected, it may be advisable, depending on the case, to relieve the bone, for example with a splint. This prevents possible bone fractures in the unstable areas.
If fibrous dysplasia causes severe pain, this is usually contained with painkillers (analgesics). A relatively new therapeutic approach is so-called bisphosphonates – drugs that are also used to treat osteoporosis and other bone diseases. They appear to have a positive effect on the bone pain and fracture tendency that accompany fibrous dysplasia and slow the progression of the disease.
In doing so, the surgeon now plans the operations using modern 3D imaging and modeling techniques, so that sensitive structures such as nerves and blood vessels are spared during the procedure.
