Fibrous Dysplasia of Bone

Fibrous dysplasia of bone is a rare condition where normal, healthy bone tissue is replaced by weaker, scar-like fibrous tissue, making bones fragile and prone to breaking or becoming misshapen.

Table of contents

• What is fibrous dysplasia of bone?
• Types of fibrous dysplasia
• What causes this condition?
• Bones most commonly affected
• Signs and symptoms
• Possible complications
• How doctors diagnose fibrous dysplasia
• Treatment options
• When to see your healthcare provider

What is fibrous dysplasia of bone?

Fibrous dysplasia is a rare bone condition that occurs when abnormal fibrous tissue (scar-like tissue) develops in place of normal bone. This fibrous tissue is not as hard as normal bone, and because it is soft and stringy, it makes the bone more fragile and prone to break.^[1] The condition weakens your bones and may increase your risk of bone fractures throughout your life.^[1]

Fibrous dysplasia is a benign (noncancerous) bone disorder. That means it won’t spread to other bones.^[1] However, the fibrous tissue can grow over time, causing the bone to become weaker.^[6] It is a chronic disorder and is often progressive. Although the lesions may stabilize and stop growing, they do not disappear.^[2]

This condition is very rare, accounting for about 7% of all benign bone tumors.^[2] It can affect any bone in the body and sometimes occurs in more than one bone.^[3] The abnormal bone begins to form before birth, but its presence is often not discovered until childhood, adolescence, or even adulthood.^[2]

Types of fibrous dysplasia

Healthcare providers classify fibrous dysplasia by the number of bones it affects:^[1]

• Monostotic fibrous dysplasia affects only one bone. This is the most common form of the condition, accounting for about 75-80% of cases.^[4] It is active while the child is growing but often becomes inactive after puberty.^[5]
• Polyostotic fibrous dysplasia affects multiple bones. It can affect more than one bone within the same limb or multiple bones throughout the body.^[2] This form is usually more severe and may remain active throughout a person’s life.^[5] For this reason, it is typically discovered earlier in life.^[2]

When the condition affects the bones in the face and skull, it is called craniofacial fibrous dysplasia.^[5]

Fibrous dysplasia may occur as part of a larger disorder. For example, McCune-Albright syndrome is characterized by polyostotic fibrous dysplasia that occurs with hormonal abnormalities and areas of darkened skin (café-au-lait spots).^[2] This syndrome is more common in girls and affects the bones, skin, and hormone levels.^[5]

What causes this condition?

Fibrous dysplasia happens when the GNAS gene changes after conception. This genetic change occurs as the baby is developing in the womb.^[3] The mutation results in a defect in osteoblast differentiation and mineralization. Osteoblasts are cells that help your bones develop and grow.^[1] This change also causes an increase in bone breakdown by large active cells called osteoclasts.^[14]

People with fibrous dysplasia carry the mutation in some, but not all, of the cells of their body, making it a mosaic disease.^[3] Experts don’t know what triggers this genetic change.^[1] Fibrous dysplasia is not hereditary. That means you can’t pass the change on to your biological children, and parents do not pass the condition to their children.^[1]

Bones most commonly affected

Fibrous dysplasia can affect any bone in the body, but it most commonly occurs in the:^[1]

• Thigh bone (femur)
• Shin bone (tibia)
• Ribs
• Skull (including facial bones)
• Upper arm bone (humerus)
• Pelvis

Signs and symptoms

You can have fibrous dysplasia without having symptoms. Some people find out they have the condition when they have X-rays for an unrelated issue.^[1] In some cases, fibrous dysplasia has no symptoms and is only diagnosed by accident during investigations for an unrelated medical problem.^[8]

When symptoms occur, fibrous dysplasia may cause the following conditions and symptoms:^[1]

• Broken bones or bone fractures
• Bone pain
• Changes in the shape of your bones or bone deformities
• Painless, swollen area on your ribs
• Curvature of the spine (scoliosis)
• Difficulty walking
• Limb length discrepancy (one leg or arm shorter than the other)

If the skull and facial bones are affected, symptoms may include:^[1]

• Bulging eyes
• Unevenness of the sides of the face
• Jaw misalignment
• Misaligned or misshapen teeth
• Nasal congestion
• Vision loss
• Hearing loss

People with fibrous dysplasia in one bone have fewer issues than if the condition affects several bones.^[1]

Individual bone lesions typically appear during the first few years of life and expand during childhood. The vast majority of clinically significant bone lesions are detectable by age 10 years, with few new and almost no clinically significant bone lesions appearing after age 15 years.^[4]

McCune-Albright syndrome symptoms

Some people with fibrous dysplasia develop hormonal problems and changes in skin color. This is known as McCune-Albright syndrome.^[8] In this syndrome, the endocrine system (hormone-producing system) and skin are also affected.^[3]

Symptoms of McCune-Albright syndrome may include:^[3]

• Reaching puberty too soon (before 10 years of age)
• Short stature
• An overactive thyroid (hyperthyroidism)
• Low levels of phosphate in the blood, leading to higher risk of bone fractures, pain, and deformity
• High levels of growth hormone
• Patches of brown-colored skin with jagged edges (café-au-lait spots)

Possible complications

The most common complication is that fibrous dysplasia increases the chance that you’ll break a bone.^[1] You may have issues with hearing or vision if it affects bones around your eyes or ears.^[1]

Fibrous dysplasia can cause a range of complications:^[8]

• If your pelvis and leg bones are affected, this may increase your risk of arthritis developing in the hip and knee joints
• Eyesight problems or other sensory problems may develop if the bones of the skull are affected

It is very rare for areas of fibrous dysplasia to become malignant or cancerous. This occurs in less than 1% of patients and is more likely to happen in patients with the polyostotic form of the condition or in patients with McCune-Albright syndrome.^[2]

How doctors diagnose fibrous dysplasia

A healthcare provider will do a physical exam. If you have pain, they’ll carefully examine the area of your body that hurts. They’ll ask when you first noticed symptoms.^[1] You will likely be asked if you have any birthmarks, and your skin may be checked for café-au-lait spots.^[6]

A diagnosis of fibrous dysplasia is confirmed by the doctor’s findings during a physical exam and the results of tests and imaging studies.^[3] Your provider may do the following tests:^[1]

• Blood tests or urine tests to check for high enzyme levels that could mean you have fibrous tissue growing in your body
• Imaging tests like X-rays, CT scans, or MRIs that may detect fibrous tissue on your bones, broken bones, or changes in the shape of your bones
• Bone scan to see if there are other bones involved and to determine the extent of bone lesions^[3]
• Biopsy to remove a sample of the fibrous tissue or your healthy bone tissue for testing. A biopsy may be necessary for diagnosis, which can typically be performed using a needle or a small incision under anesthesia^[6]

Blood tests may be performed to determine if you have a hormonal disturbance.^[6]

Treatment options

Your treatment will depend on your symptoms and how the condition affects you.^[1] Treatment depends on the location and the amount of bone involved.^[6] If there is a small area of bone involved that is unlikely to break and there is no associated pain, it can be monitored.^[6]

The most common fibrous dysplasia treatments are:^[1]

• Observation. You might not need any treatment other than follow-up appointments with your healthcare provider. They’ll watch for any changes in your bone health.
• Medication. Providers may prescribe drugs that strengthen your bones and help prevent fractures. Bisphosphonates may be used to help treat pain and reduce bone breakdown. These are medications that are known to reduce bone pain and reduce the risk for fractures.^[14] Recent clinical trials have shown that a medication called denosumab significantly reduced abnormal bone turnover in adults with fibrous dysplasia and may improve patients’ quality of life by enabling healthy bone formation.^[13]
• Bracing. Wearing braces can support your bones and help them grow correctly.
• Surgery. You may have surgery to treat broken bones, including bone grafts. Surgery is still the standard treatment for fractures and deformities caused by fibrous dysplasia.^[13] Surgery may also be necessary to prevent deformities or limb-length discrepancies from occurring.^[6]

During surgery, bone that is obtained from an organ donor (cadaveric, allograft bone) may be used to replace the abnormal bone. Bone substitutes made from a form of calcium may be considered as well. There is a risk that the bone or bone substitute can be reabsorbed and the fibrous dysplasia may come back.^[6]

If hormonal disturbances are discovered, you may be referred to an endocrinologist (a doctor who specializes in hormone-related conditions) for further treatment.^[6]

When to see your healthcare provider

You should talk to a healthcare provider if you have bone pain that doesn’t go away. If you have fibrous dysplasia, talk to your provider if you feel like your symptoms are getting worse or if it seems that treatments aren’t making a difference.^[1]

If there is any new growth, pain, or other symptoms that develop, it should be checked immediately.^[6]