Polyostotic fibrous dysplasia MRI

Polyostotic fibrous dysplasia is a rare bone disorder where normal bone and bone marrow are replaced by fibrous tissue, leading to structurally weak, misshapen, and brittle bones. This condition is polyostotic when it affects multiple bones in the body, distinguishing it from monostotic fibrous dysplasia, which affects only one bone. It is one of the manifestations of the McCune-Albright syndrome but can also occur in isolation.

Causes

Polyostotic fibrous dysplasia is caused by a mutation in the GNAS gene, which encodes a protein involved in the regulation of cyclic AMP (cAMP) in cells. This mutation occurs after conception, in the early stages of fetal development (a post-zygotic mutation), meaning it is not inherited from the parents but occurs sporadically. The mutation leads to overactivity of bone-forming cells (osteoblasts), causing the abnormal bone growth and lesions characteristic of the disease.

Symptoms

Symptoms of polyostotic fibrous dysplasia vary depending on the number and location of bones involved but typically include:

• Bone pain and deformities
• Bone fractures
• Uneven growth of limbs
• Scoliosis or other spinal deformities
• Skin pigmentation (café-au-lait spots), especially when part of McCune-Albright syndrome

Diagnosis

Diagnosing polyostotic fibrous dysplasia usually involves a combination of clinical examination, imaging, and possibly genetic testing:

• X-rays: Show characteristic changes in bone, such as irregular, cyst-like areas or “ground glass” opacity.
• Bone scan: Helps in identifying the extent and activity of the disease.
• MRI or CT scans: Provide detailed images of bone and can help in assessing the extent of bone deformity and planning surgical interventions.
• Biopsy of bone tissue: Confirms the diagnosis by showing the replacement of normal bone with fibrous tissue and abnormal bone.
• Genetic testing: Can identify mutations in the GNAS gene, especially useful in cases where the diagnosis is uncertain.

Treatment

Treatment for polyostotic fibrous dysplasia is usually symptomatic and aimed at managing pain, preventing fractures, and correcting deformities:

• Medication: Bisphosphonates can help reduce bone pain by decreasing bone turnover.
• Surgery: May be necessary to correct bone deformities, fix fractures, or stabilize bones at risk of fracturing.
• Pain management: Includes the use of analgesics and anti-inflammatory drugs.
• Hormonal therapy: If the disease is part of McCune-Albright syndrome, endocrine abnormalities such as precocious puberty or hyperthyroidism may need treatment.
• Physical therapy: Helps strengthen muscles around affected bones and improve mobility.