June 2015
What Is Fibrous Dysplasia?
Fibrous dysplasia (FD) is a skeletal disorder in which bone-forming cells fail to mature and produce too much fibrous, or connective, tissue. Areas of healthy bone are replaced with this fibrous tissue. The replacement of normal bone in fibrous dysplasia can lead to pain, misshapen bones, and fracture, especially when it occurs in the long bones (arms and legs). When it occurs in the skull, there can also be a replacement of the normal bone with fibrous tissue, resulting in changes in the shape of the face or skull, pain, and, in rare circumstances, hearing or vision loss.
Some people with fibrous dysplasia have only one bone involved (monostotic), whereas other people have more than one bone involved (polyostotic). The disease may occur alone, or as part of a condition known as the McCune-Albright syndrome. McCune-Albright syndrome is characterized by fibrous dysplasia and other symptoms such as patches of pigmented skin (light brown or “café-au-lait” spots) and endocrine problems such as early puberty (precocious puberty), hyperthyroidism (excess thyroid hormone), excess growth hormone (gigantism or acromegaly), excess cortisol (Cushing’s syndrome), and other rare conditions.
Fibrous dysplasia can affect any bone in the body. The most common sites are the bones in the skull and face, femur (thighbone), tibia (shinbone), humerus (upper arm), pelvis, and ribs. Although many bones can be affected at once—and affected bones are often found on one side of the body—the disease does not “spread” from one bone to another; that is, the pattern of which bones are involved is established very early in life and does not change with age.