Fibrous dysplasia is an uncommon bone disorder in which scar-like (fibrous) tissue develops in place of normal bone. This irregular tissue can weaken the affected bone and cause it to deform or fracture.

In most cases, fibrous dysplasia occurs at a single site in one bone, but can occur at multiple sites in multiple bones. Single bone involvement usually occurs in adolescents and young adults. People who have more than one affected bone typically develop symptoms before the age of 10.

Although fibrous dysplasia is a genetic disorder, it's caused by a gene mutation that's not passed from parent to child. There's no cure for the disorder. Treatment, which may include surgery, focuses on relieving pain and repairing or stabilizing bones.

Fibrous dysplasia may cause few or no signs and symptoms, particularly if the condition is mild. More severe fibrous dysplasia may cause:

• Bone pain, usually a mild to moderate dull ache
• Swelling
• Bone deformity
• Bone fractures, particularly in the arms or legs
• Curvature of leg bones

Fibrous dysplasia can affect any bone in the body, but the most commonly affected bones include the following:

• Thighbone (femur)
• Shinbone (tibia)
• Upper arm bone (humerus)
• Skull
• Ribs
• Pelvis

Rarely, fibrous dysplasia may be associated with a syndrome that affects the hormone-producing glands of your endocrine system. These abnormalities may include:

• Very early puberty
• Overactive hormone production
• Light brown spots on the skin

Increased bone pain also may be associated with the normal hormonal changes of the menstrual cycle or pregnancy.

When to see a doctor

See your doctor if you or your child develops any of the following:

• Bone pain that increases with weight-bearing activity or doesn't go away with rest
• Bone pain that interrupts sleep
• Difficulty walking or limping
• Unexplained swelling
• Changes in bone shape
• Difference in limb length

Fibrous dysplasia is linked to a gene mutation present in certain cells that produce bone. The mutation results in the production of immature and irregular bone tissue. Most often the irregular bone tissue (lesion) is present at a single site on one bone. Less often multiple bones are affected, and there may be more than one lesion on multiple bones.

A lesion usually stops growing sometime during puberty. However, lesions may grow again during pregnancy.

The gene mutation associated with fibrous dysplasia occurs after conception, in the early stages of fetal development. Therefore, the mutation isn't inherited from your parents, and you can't pass it on to your children.

Severe fibrous dysplasia can cause:

• Bone deformity or fracture. The weakened area of an affected bone can cause the bone to bend. These weakened bones also are more likely to fracture.
• Vision and hearing loss. The nerves to your eyes and ears may be surrounded by affected bone. Severe deformity of facial bones can lead to loss of vision and hearing, but it's a rare complication.
• Arthritis. If leg and pelvic bones are deformed, arthritis may form in the joints of those bones.
• Cancer. Rarely, an affected area of bone can become cancerous. This rare complication usually only affects people who have had prior radiation therapy.

The primary tool for diagnosis of fibrous dysplasia is an X-ray. While bone appears solid in an X-ray, a fibrous dysplasia lesion has a relative distinct appearance often described as "ground glass." The condition may be diagnosed, therefore, even in a person with no symptoms who is getting an X-ray for other reasons.

An X-ray can also help your doctor determine how much of the bone is affected and whether there is any deformity in the bone.

Additional tests may be used to confirm a diagnosis or rule out other disorders:

• Imaging tests. Computerized tomography and magnetic resonance imaging can produce cross-sectional or 3-D images of bone. These tools can help your doctor better characterize the quality of bone or a fracture associated with fibrous dysplasia.
• Bone scan. A bone scan is a nuclear imaging test. A small amount of radioactive tracer is injected into your bloodstream and taken up by damaged portions of bone. When your body is scanned with a specialized camera, the images can help a doctor identify multiple fibrous dysplasia lesions.
• Biopsy. This test uses a hollow needle to remove a small piece of the affected bone for microscopic analysis. The structure and arrangement of cells can confirm a fibrous dysplasia diagnosis.

If you have mild fibrous dysplasia that's discovered incidentally and you have no signs or symptoms, your risk of developing deformity or fracturing your bone is low. Your doctor will likely monitor your condition with periodic X-rays.

Medications

Osteoporosis medications called bisphosphonates help prevent bone loss by decreasing the activity of cells that normally dissolve bone. Some studies suggest that bisphosphonates may strengthen bones affected by fibrous dysplasia and may relieve bone pain.

Surgery

Your doctor may recommend surgery in order to:

• Correct a deformity
• Correct a difference in limb lengths
• Repair a fracture that does not heal with casting
• Prevent fractures
• Relieve pressure on a nerve, particularly if the lesion is in your skull or face

Surgery may involve removing the bone lesion and replacing it with a bone graft: bone from another part of your body, bone tissue from a donor or a synthetic material. In some cases a fibrous dysplasia lesion may develop again.

Your surgeon also may insert metal plates, rods or screws to prevent fractures or to stabilize a bone or bone graft.

Most people with fibrous dysplasia don't have symptoms and are diagnosed when an X-ray taken for another reason reveals signs of fibrous dysplasia.

However, in some cases you or your child may experience pain or other symptoms that lead you to schedule an appointment with your family doctor or your child's pediatrician. In some cases, you may be referred to a doctor who specializes in treating bone and muscle injuries or disorders (orthopedic surgeon).

What you can do

Before your appointment, you might want to compose a list of answers to the following questions and be ready to discuss them with your doctor:

• When did symptoms begin?
• How severe are the symptoms?
• Have symptoms been continuous or occasional?
• Does any specific activity make the symptoms worse?
• Does anything relieve symptoms?
• Does pain wake you or your child at night?
• Is the pain or deformity getting better, staying the same or getting worse?
• What medications or supplements do you or your child take regularly?