Fibrous Dysplasia

Overview

Fibrous dysplasia is an uncommon bone disorder in which areas of normal bone are replaced by a softer, scar-like (fibrous) tissue mixed with abnormal bone. These patches are weaker than healthy bone, so they can bend, expand, or break. The disorder is not cancer and does not usually spread, but it can cause pain and deformity.

Fibrous dysplasia can affect a single bone (monostotic), which is the most common form, or several bones (polyostotic). When it occurs together with hormone problems and patches of skin discoloration, it is part of a condition called McCune-Albright syndrome. The disorder is present because of a gene change that happens during early development; it is not inherited from a parent and cannot be passed to children.

Symptoms

Many people with mild fibrous dysplasia have no symptoms, and the condition is found by chance on an X-ray taken for another reason. When symptoms occur, they depend on which bones are involved.

• Bone pain, often a dull ache that may worsen with activity
• Visible deformity, such as a curved leg or an uneven face or skull
• Bones that break easily (fractures), sometimes with little injury
• Limping or difficulty walking if a leg bone is affected
• Hearing or vision changes if bones around the ear or eye are involved

In McCune-Albright syndrome there may also be early puberty, light-brown skin patches, and other hormone-related signs.

Causes

Fibrous dysplasia is caused by a change (mutation) in a gene called GNAS. This change occurs randomly in a single cell early in development, after conception. As that cell multiplies, the affected bone-forming cells produce disorganized, fibrous bone instead of strong, normal bone.

Because the change happens after conception and is present only in some cells, fibrous dysplasia is not inherited and is not passed from parent to child. It is not caused by diet, injury, or anything a person did or was exposed to.

Risk Factors

Fibrous dysplasia has no known preventable risk factors and is not linked to family history, since the underlying gene change is not inherited. The extent of disease ranges widely:

• A single affected bone, often discovered in adolescence or adulthood
• Multiple affected bones, which tend to be recognized earlier in childhood
• Association with McCune-Albright syndrome in a small share of cases

Diagnosis

Diagnosis usually starts with imaging and may be confirmed with a tissue sample:

• X-rays: Affected bone often has a hazy, ground-glass appearance that is characteristic of fibrous dysplasia.
• CT or MRI: Show the size and exact location of lesions and how much bone is involved.
• Bone scan: Helps find all the affected sites when several bones may be involved.
• Biopsy: Occasionally needed to confirm the diagnosis or rule out other bone conditions.
• Blood and hormone tests: Used when McCune-Albright syndrome is suspected.

Treatment

There is no cure that removes fibrous dysplasia entirely, so treatment focuses on relieving pain, preventing fractures, and correcting deformity.

• Monitoring: Mild, symptom-free disease may simply be watched with periodic imaging.
• Pain medication: Over-the-counter pain relievers help with mild discomfort.
• Bisphosphonate medicines: These bone-strengthening drugs can reduce bone pain in some people.
• Surgery: Used to repair or prevent fractures, correct deformity, or remove tissue that is pressing on nerves; metal rods or grafts may be used to stabilize weak bone.
• Treating related hormone problems: Needed when fibrous dysplasia is part of McCune-Albright syndrome.

Because lesions can change over time, long-term follow-up is recommended.

Prevention

Fibrous dysplasia cannot be prevented, because the gene change that causes it occurs by chance during early development. Practical care focuses on protecting weakened bones: staying active in safe ways to maintain strength, addressing vitamin D and calcium needs as advised, and treating pain early so that activity does not lead to a fracture.

When to See a Doctor

See a doctor for persistent bone pain, a new bone deformity, or a bone that breaks easily. Seek prompt care if a bone fractures after little or no injury, or if you notice new vision changes, hearing loss, or facial swelling, which may mean a lesion is affecting bones around the eye or ear.

Related Topics

Frequently Asked Questions

References

1. National Institutes of Health (NIH), Genetic and Rare Diseases Information Center. Fibrous dysplasia.
2. Mayo Clinic. Fibrous dysplasia.
3. MedlinePlus, U.S. National Library of Medicine. Fibrous dysplasia.
4. American Academy of Orthopaedic Surgeons (OrthoInfo). Fibrous Dysplasia.