Fibrous Dysplasia

What is Fibrous Dysplasia?

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

What are the symptoms of Fibrous Dysplasia?

Fibrous dysplasia may cause few to no signs or 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

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.

What causes Fibrous Dysplasia?

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.

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

How is Fibrous Dysplasia diagnosed?

The primary tool for diagnosis 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.”

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 doctors better characterize the quality of bone or a fracture associated with fibrous dysplasia.
Bone scan – A small amount of radioactive tracer is injected into the bloodstream and taken up by damaged portions of bone. When 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.

What are the treatments for Fibrous Dysplasia?

The drug tocilizumab is being studied as a potential therapy for FD. Tocilizumab is a drug that works by blocking the activity of interleukin-6 (IL-6), a specialized protein (cytokine) that stimulates bone resorption.

Affected bone cells in Fibrous Dysplasia release excess levels of interleukin-6 and researchers believe inhibiting IL-6 will decrease bone resorption.