Published: 18 Jun 2025

ICD9: 756.54      ICD10: M85.00      ICD11: XH5FY2

Fibrous dysplasia (FD) is a rare, benign (noncancerous) bone disorder in which normal bone and marrow are replaced with fibrous, scar-like tissue.
This replacement weakens the bone and can lead to pain, fractures, deformities, and other problems.

Here's a breakdown of key aspects of fibrous dysplasia:

What Happens:

Abnormal Bone Development: Instead of normal bone cells forming properly, they are replaced by a mix of fibrous tissue (like scar tissue) and poorly organized, immature bone.
Weakened Bones: This abnormal tissue is weaker than normal bone, making the affected bones prone to fractures, bending, and deformities.
Variable Severity: The severity can range from a small, asymptomatic lesion to extensive involvement affecting multiple bones and organs.

Causes:

Genetic Mutation: FD is caused by a genetic mutation in the *GNAS1* gene. This mutation typically occurs spontaneously (not inherited) early in embryonic development. Therefore, it is almost always *not* passed down from parents to children.

Types:

Monostotic FD: This is the most common form. It affects a *single* bone. The ribs, femur (thigh bone), tibia (shin bone), jaw, and skull are commonly involved.
Polyostotic FD: This affects *multiple* bones. It tends to be more severe than monostotic FD.
McCune-Albright Syndrome: This is a rare and more severe form of polyostotic FD that is associated with:
Polyostotic FD: Multiple bones are affected.
Endocrine Abnormalities: These can include precocious puberty (early puberty) in girls, hyperthyroidism (overactive thyroid), acromegaly (excess growth hormone), and Cushing's syndrome (excess cortisol).
Café-au-lait Spots: These are light brown, flat birthmarks on the skin with irregular borders (often described as "coast of Maine").

Symptoms:

Symptoms vary depending on the location and extent of the affected bone(s). They may include:

Bone Pain: Aching, throbbing, or sharp pain in the affected bone.
Bone Deformities: Bowing of the legs, curvature of the spine (scoliosis), facial asymmetry, or other bone distortions.
Fractures: Increased susceptibility to fractures, even from minor injuries.
Limp: If the leg bones are affected.
Headaches, Vision Problems, Hearing Loss: If the skull is involved, the growing bone can press on nerves.
Endocrine Problems: (In McCune-Albright syndrome) Precocious puberty, thyroid problems, etc.

Diagnosis:

X-rays: Often show characteristic "ground glass" appearance in the affected bone.
CT Scans: Provide more detailed images of the bone structure.
Bone Scans: Can help identify areas of increased bone activity.
Biopsy: A small sample of the affected bone is taken and examined under a microscope to confirm the diagnosis.
Genetic Testing: Can be performed to identify the *GNAS1* mutation, but it's not always necessary for diagnosis.

Treatment:

There is no cure for fibrous dysplasia. Treatment focuses on managing symptoms and preventing complications:

Pain Management: Pain relievers (over-the-counter or prescription).
Bisphosphonates: Medications that can help strengthen bones and reduce pain (e.g., alendronate, zoledronic acid).
Orthotics/Braces: To support affected limbs and prevent deformities.
Surgery: May be necessary to:
Correct deformities.
Stabilize fractures.
Remove lesions that are causing pain or pressing on nerves.
Prevent fractures (prophylactic fixation).
Monitoring: Regular checkups and imaging studies to monitor the progression of the disease and detect any complications.
Treatment of Endocrine Problems: (In McCune-Albright syndrome) Management of precocious puberty, thyroid problems, etc., by specialists.

Prognosis:

The prognosis varies depending on the extent and severity of the disease.

Monostotic FD: Often has a good prognosis. Symptoms can often be managed with conservative treatment.
Polyostotic FD: Can be more challenging to manage. Deformities and fractures can be a significant problem.
McCune-Albright Syndrome: Has the most complex prognosis due to the involvement of multiple systems.

Important Points:

Fibrous dysplasia is *not* cancer.
It is *not* contagious.
It is usually *not* inherited.
Treatment is aimed at managing symptoms and preventing complications.

If you suspect you or someone you know has fibrous dysplasia, it's essential to consult with a qualified healthcare professional, such as an endocrinologist, orthopedic surgeon, and/or geneticist, for proper diagnosis and management. They can provide personalized advice based on the specific situation.