Fibrous dysplasia (FD) is a bone disease characterized by areas of abnormal growth or lesions in one, several, or many bones. FD can occur in any bone. The skull frequently is affected as are legs, arms, and ribs. The majority (about 70%) of people with FD have only one bone site involved, a condition called monostotic FD. When FD is in more than one bone it is called polyostotic FD or PFD. About 10% of those with polyostotic FD have some associated endocrine (hormonal) problems including precocious puberty and areas of increased skin pigment called cafe-au-lait marks. These birthmarks have irregular borders like the coast of Maine and, like the bone lesions, may be primarily on one side of the body. The combination of polyostotic fibrous dysplasia, endocrine disorders, and café-au-lait marks is called McCune Albright Syndrome (MAS).
McCune-Albright Syndrome is named for the two physicians who described it over 50 years ago. They reported a group of children, most of them girls, with an unusual pattern of associated abnormalities: bone disease, with fractures, asymmetry and deformity of the legs, arms, and skull; endocrine disease, including early puberty with menstrual bleeding, development of breasts and pubic hair and an increased rate of growth; and skin changes, with areas of increased pigment distributed in an asymmetric and irregular pattern. Today, the term "McCune-Albright syndrome" is used to describe patients who have some or all of these bone, endocrine, and skin abnormalities. In the years since it was first identified, however, researchers have studied many additional patients, and have learned that the condition has a broad spectrum of severity. Sometimes, children are diagnosed in early infancy with obvious bone disease and markedly increased endocrine secretions from several glands; a very few of these severely affected children have died. At the opposite end of the spectrum, many children are entirely healthy, and have little or no outward evidence of bone or endocrine involvement. They may enter puberty close to the normal age, and have no unusual skin pigment at all.
What are the similarities of Fibrous Dysplasia with other diseases?
There are a number of diseases that have simlilar sounding names or or similar features, but are not fibrous dysplasia. The following provides a brief synopsis of one of these diseases.
Cherubism is a rare, familial, painless disorder characterized by enlargement of the upper and lower jaw bones (maxilla and mandible) on both sides of the face (bilateral). The disease is transmitted in an autosomal dominant fashion. Those affected by the disease have unusual chubbiness and swelling of the face. The facial changes can vary considerably from person to person; they can be very mild to severely disfiguring. The facial changes are brought about by overgrowth of fibrous tissue around the jaw bones. The disease starts to appear in the 3rd or 4th year of life and continues to grow until the person affected reaches the age of 15-20. The size of the jaw then stabilises and progressively becomes smaller until it is hardly noticeable. Fibrous dysplasia and Cherubism have several features in common but differences also exist between these diseases. At times, it can be difficult to tell the difference between the two.
What are the Symptoms of Fibrous Dysplasia and McCune-Albright Syndrome?
Some people with FD may have no symptoms; the bone lesions may be found only because an X-ray was done for some other reason. Others, especially those with more bones involved, may have many. These symptoms may include pain, enlargement or deformity of the bone, and increased occurances of fractures due to the weakened bone. Very rarely the bone deformities may affect the ability to walk, if in the weight-bearing parts of the skeleton, or the function of nerves in the head that control vision or other senses. Those who have MAS may have a variety of endocrine problems such as early puberty or over-production of thyroid hormones.
FD is not hereditary. We did not get FD from our parents and we cannot pass it on to our children. FD is caused by a mutation that occurs sometime during development of a baby while it is still in the mother's uterus. If the mutation occurs early in development, many tissues may be affected. If it occurs late in development, very few tissues may have the mutation. Because the mutation occurs before birth, FD is considered a genetic disease. But unlike almost all other diseases it is not hereditary because it cannot exist in sperm or egg cells.
We do not know why the FD mutation occurs. The gene involved in FD seems to be especially susceptible to mutations. Although FD is rare, it occurs in males and females and in people of all races and from all parts of the world. It is possible that the mutation occurs randomly.
The doctor called my Fibrous Dysplasia a tumor. Do I have cancer and can it become malignant?
FD is not cancer. "Tumor" simply means abnormal growth. Tumors can be malignant (cancerous) or benign (non-cancerous). Many people prefer to use to term "lesion" generally meaning any defect to avoid confusion of FD with malignant bone tumors.
Usually, for a cancer to form, several mutations have to occur in the same cell over time. The same mutation that causes FD has been found in a few pituitary cancers and very rarely in thyroid cancer. Since most people with FD do not have these cancers, the FD mutation does not seem to cause cancers by itself. It is possible for an FD bone lesion to become cancerous; but this is very rare, occurring in less than 1% of FD cases.
The doctor said Fibrous Dysplasia would subside after my teen years. Is this true?
Older medical texts often suggested that FD lesions would stop growing once a child reached full adult stature. Many people do experience fewer problems with FD after puberty, especially with FD lesions in the legs and arms. However, some people continue to have problems with their FD beyond puberty and first diagnosis of FD may occur in adulthood.
I often feel pain with my Fibrous Dysplasia but the doctor said there is no pain associated with the disease. Is this true?
Unfortunately, some older medical textbooks stated that FD lesions are painless and some doctors assume that this is the case. Many people with FD lesions do not have much pain, but many others do. Pain seems to be less common in children than in adults; but anyone with FD can experience pain when a lesion fractures, with surgery or with some other activities. Some have noticed that their pain is worse with certain weather changes.
Is there a cure for the disease so I can get rid of Fibrous Dysplasia for good?
In general, FD cannot be cured at the present time. The only exception is if there is only one lesion in one bone and that lesion is completely eliminated by surgery. Often there are unidentified FD cells in several bones and it is not possible to eliminate all of these by surgery. Some drug treatments are being identified that significantly diminish bone pain in long bones (arms, legs, ribs) and may cause some good bone to fill in the defects. Bisphosphonate drugs such as alendronate (Fosamax) that is used for treating osteoporosis or pamidronate (Aredia) have been helpful for some people. These drugs are not effective in all people with FD; but researchers are continuing to investigate other possible treatments.
How is Fibrous Dysplasia going to affect my life now and in the future?
There is no simple answer for this question. The effects of Fibrous Dysplasia are as different as each person who has it. For some people, it has no impact at all, while others are so intensely impacted by FD that they are forced to use a cane or a wheelchair, and have become disabled in some way, such as in partial loss of vision or mobility. Therefore, it is best to know exactly where your Fibrous Dsyplasia exists and to regularly monitor its presence with medical check-ups. If you are aware of what is happening to your body, you are in a better position to control or minimize the impact of FD on you life now and in the future.
Among bone tumors, FD is fairly common; but it is a rare disease in the general population. Based on statistics from the FDSOL membership as of 2000, an indicence of one person with FD out of every 15,000 - 30,000 people has been estimated. This estimate includes only people whose FD causes symptoms that lead to a diagnosis using current medical technology. Is is difficult to be sure how many might have the disease but will never know it because they will not experience the complications that will lead to a diagnosis. The estimated incidence suggests that between 9,000 and 18,000 people in the US will have a diagnosis of FD in their lifetime.
What bones are most affected by Fibrous Dysplasia?
Any bone can be affected by Fibrous Dysplasia. Patients with only one bone site involved are diagnosed as having Monostotic FD while patients with numerous affected bones are diagnosed as having Polyostotic FD.
This topic was explored as part of the analysis of the FDSOL database performed in the year 2000. Those registering with Polyostotic FD (or MAS) did not have an opportunity to indicate all their affected bone sites when registering, so the study focused on all members who had registered as being diagnosed with Monostotic FD only.
The distribution of bone sites for the 318 members with Monostotic FD is as follows:
An interesting finding from the analysis is that patients diagnosed with Monostotic FD were as likely to have the effected bone site in the skull (46%) as with all other bones in the body combined (54%). This appears to be somewhat significant since the skull contains only 29 of the body's 206 bones and is a proportionately smaller bone mass when compared to the rest of the skeleton. There did not appear to be any difference in the reported bone sites between men and women with Monostotic FD.