What is Fibrous Dysplasia?

Fibrous dysplasia is a chronic disorder of the skeleton that causes expansion of one or more bones due to abnormal development of the fibrous, or connective, tissue within the bone. The abnormality will cause uneven growth, brittleness and deformity in affected bones. Some patients have only one bone affected (monostotic), whereas other patients have numerous bones affected (polyostotic). While any bone can be affected by fibrous dysplasia, the most common sites of the disease are the femur (thigh bone), tibia (shin bone), ribs, skull, facial bones, humerus (upper arm), and pelvis. The vertebrae are less frequently involved. Although many bones can be affected at once, fibrous dysplasia is not a disease that spreads from one bone to another. Multiple affected bones are often found on one side of the body.
 

Who is Affected?

Fibrous dysplasia is a very uncommon disorder, and the total number of cases is not known. It is usually diagnosed in children and young adults. If the disease involves more than one bone, it is more likely to produce problems before age 10. The disease is found equally in males and females and does not appear to vary in incidence among races.
 

What is the Cause?

Recent studies indicate that fibrous dysplasia may be caused by a chemical abnormality in a protein in the bone that leads to an overgrowth of bone cells that produce fibrous tissue. The chemical abnormality occurs because of a mutation or change in the structure of the gene that produces the protein. Fibrous dysplasia is thought to be a congenital disorder, meaning that individuals who have it probably had it when they were born. There is no evidence, however, that the disorder can be inherited.
 

Symptoms

Depending on where a patient has fibrous dysplasia, various problems can develop. The most common are:

• Bone Pain: Bone pain may occur due to the expanding fibrous tissue in the bone. The onset of pain may signal an impending fracture in a bone that has been weakened by this gradual expansion. A fracture may cause a sudden increase in severe pain. It is also possible, although less common, for abnormal bone to produce pain by pressing on an adjacent nerve. In patients with considerable deformity of the weight-bearing long bones (thighs and shins), arthritis can develop in the hips and knees.
• Bone Deformity: Because fibrous dysplasia can affect any bone, bone deformity can occur anywhere in the skeleton. Bone deformity caused by fibrous dysplasia is most obvious when it occurs in the skull and facial bones. Fibrous dysplasia of the skull may cause loss of vision and hearing.
• Fracture: When a bone is affected by fibrous dysplasia, the fibrous, or connective, tissue expands while the bone surrounding the fibrous tissue breaks down. Therefore, even though the fibrous tissue thickens, the bone itself becomes thin and fragile and fractures can occur. This occurs most often in the long bones of the legs.
• McCune-Albright Syndrome
  Some individuals with fibrous dysplasia also may develop hormonal problems such as early puberty, hyperthyroidism, excessive secretion of several pituitary hormones, and high blood calcium from parathyroid hormone. Individuals with hormonal disturbances also may exhibit areas of darkly pigmented skin called "café-au-lait," or "coffee-milk" spots. The combination of fibrous dysplasia, hormonal disturbances, and skin pigmentation is called McCune-Albright syndrome, named for Dr. Donovan McCune and Dr. Fuller Albright, who independently described the syndrome in 1937. Patients who have fibrous dysplasia in only one bone usually do not develop McCune-Albright syndrome. The genetic abnormality that has been found in bone is also found in other tissues that have abnormal function.
   
  

Symptoms of Hormonal Disturbance

(See glossary for explanation of terms)

• Early puberty: Signs of early puberty can include menstruation or the development of other secondary sex characteristics, such as breast development or an enlarged penis before age 10.
• Hyperthyroidism: When a person's thyroid gland is overactive, he or she suffers from hyperthyroidism. Signs of hyperthyroidism include anxiety, excessive sweating and weight loss.
• Overactivity of the adrenal glands: Weight gain, a red face, muscle weakness and high blood sugar may indicate overactivity of the adrenal glands.
• Oversecretion of pituitary hormones: Signs of oversecretion of pituitary hormones could include milk production in the breasts of women who have not been pregnant recently; gigantism, or extreme height beginning before puberty; and acromegaly, or extreme fleshiness beginning after puberty.
• High blood calcium from parathyroid hormone: Nausea, vomiting, constipation and impaired mental function may be indicators of a high blood calcium level due to excessive production of parathyroid hormone.
• Rickets: In rare instances, children with fibrous dysplasia may experience impaired growth and develop skeletal deformities due to rickets.
   
  Diagnosis
  The bones affected by fibrous dysplasia usually have a characteristic appearance on X-ray. When there is doubt about the diagnosis, a doctor may obtain a small bone specimen for examination by a pathologist.

Treatment

Types of Physicians
Most commonly, patients with fibrous dysplasia are evaluated and treated by:

• Orthopedic surgeons, since most symptomatic patients have bone pain and/or skeletal deformity;
• Craniofacial or plastic surgeons who are needed for correction of facial deformities;
• Neurosurgeons who are needed for treatment of brain or spinal complications; and
• Endocrinologists who are best for treating patients who develop hormonal problems.

Surgery

Surgery is recommended for fibrous dysplasia to relieve intractable bone pain, to improve mobility that may be impaired due to skeletal deformity, to facilitate the healing of fractures, to relieve local pressure on the spinal cord, spinal nerves, or brain, and to treat the unusual complication of bone sarcoma. Some of the surgical procedures commonly used are:

• Removal of affected bone followed by bone grafting in patients with persistent bone pain
• Removal of a wedge of bone with placement of pins and bone grafts to correct deformities.
  Non-Surgical Treatments
  Pamidronate (Aredia®) is a bisphosphonate drug approved by the Food and Drug Administration (FDA) for several disorders including hypercalcemia, Paget's disease of bone, breast cancer metastatic to bone and multiple myeloma. Studies have shown that some individuals with fibrous dysplasia may have considerable benefit from this therapy, though it is not specifically approved for the treatment of fibrous dysplasia. Multiple intravenous infusions of pamidronate have been reported to relieve bone pain and lessen the extent of the disease in some patients with fibrous dysplasia.

Prognosis

There is a great variability in the clinical course of this disorder. Young patients who have fibrous dysplasia in many bones may have more problems. Patients with one or only a few lesions may have mild or no symptoms. Related hormonal abnormalities are usually successfully treated once a problem is recognized.

The Benefits of Exercise

Exercise is very important in maintaining skeletal health and is recommended for patients with fibrous dysplasia. Exercise is also helpful in avoiding weight gain and in maintaining mobility of the joints. The exercise program should be carefully designed under physician supervision to minimize risk of fracture.
 

Glossary of Terms

• Adrenal Glands: The adrenal glands are two hormone-secreting glands located directly above the kidneys. The adrenal glands help to regulate the body's use of carbohydrates, fat, sugar and protein and also control the body's response to stress.
• Bisphosphonates: Medications that inhibit or slow the breakdown of bone.
• Cranial: Pertaining to the bones of the head.
• Endocrinologists: Physicians who specialize in hormonal and metabolic disorders.
• Fibrous: Composed of or containing fibroblasts, or cells present in connective tissue capable of forming collagen fibers.
• Gene: A functional unit of heredity that occupies a specific place on a chromosome and is capable of reproducing itself exactly at each cell division.
• Hypercalcemia: An abnormally high concentration of calcium compounds in the blood.
• Hypothalamus: The part of the brain that functions to regulate body temperature, certain metabolic processes and other involuntary activities.
• Parathyroid Gland: The parathyroid glands are located adjacent to the thyroid gland and control the metabolism of calcium in the body.
• Pituitary Gland: Located at the base of the skull beneath a section of the brain called the hypothalamus, the pituitary gland is the most important hormone-secreting gland in the body. It not only controls other hormone-secreting glands like the thyroid and adrenal glands, but it is also essential for many normal bodily functions.
• Rickets: A disease due to vitamin-D deficiency and characterized by overproduction and deficient calcification of osteoid tissue, with associated skeletal deformities and disturbances in growth. Usually accompanied by irritability, listlessness and generalized muscular weakness. Fractures are frequent.
• Sarcoma: A body of connective tissue, usually highly malignant.
• Thyroid Gland: The thyroid gland is a hormone-secreting gland located at the lower portion of the front of the neck. The thyroid regulates metabolism and is essential for normal mental and physical development. Revision Date: 8/2000

The NIH Osteoporosis and Related Bone Diseases ~ National Resource Center is supported by the
National Institute of Arthritis and Musculoskeletal and Skin Diseases
with contributions from the National Institute of Child Health and Human Development, National Institute of
Dental and Craniofacial Research, National Institute of Diabetes and Digestive and Kidney Diseases,
NIH Office of Research on Women's Health, DHHS Office on Women's Health, and National Institute on Aging.