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.

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.