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Introduction
Fibrous dysplasia happens when abnormal fibrous (scar-like) tissue replaces healthy bone. The fibrous tissue weakens the bone over time, which can lead to fractures (breaks) and misshapen bones.
Definition
Waldron 1985 A benign lesion, presumably developmental in nature, characterized by the presence of fibrous connective tissue with a characteristic whorled pattern and containing trabeculae of immature non lamellar bone..
Reeds definition fibrous dysplasia is an arrest of bone maturation in woven bone with ossification resulting from metaplasia of a non specific fibro-osseous type
Types
- One bone (monostotic).
- Multiple affected bones (polyostotic)
- Craniofacial form
Etiology
- Fibrous dysplasia is not hereditary in nature
- It caused by mutation in the GNAS1 (guanine nucleotide binding protein, alpha stimulating activity polypeptide) gene and this gene encodes a G-protein which results in overproduction of cAMP in the affected tissues.
- Thus ,there is increased the proliferation of melanocytes thus results in cafe-au-lait spots.
- The cAMP have effect on the differentiation of osteoblasts
Pathophisiology
- Bianco et al demonstrated that FD is a disease of bone marrow stromal cells (BMSC)
- The BMSCs form structural framework upon which hematopoiesis occurs in the bone marrow and a subset of BMSC are multipotent stem cells capable of differentiating into multiple cells including osteoblasts, osteocytes, chondrocytes, bone marrow adipocytes and other cells.
- In FD BMSC differentiate along osteogenic lineage, but differentiation is arrested and instead undergo proliferation giving rise to fibro-osseous masses of tissue.
- Arrest in differentiation is by mutation in GNAs gene.
Clinical Features
- Incidence 1:4000 to 1:10,000
- Some people do not have symptoms
- Fatigue, particularly in young children
- Pain and weakness in the areas affected
- Fractures or breaks
- Misshapen bones (bone deformity)
- Cafe au lait spots
- Signs and symptoms of underlying endocrine disorders such as growth hormone excess, overactive thyroid and early puberty
- Female patients experience increased pain level during pregnancy and during the menstrual cycle because of estrogen receptors found in FD.
- Symptoms may range from mild to severe. Some symptoms may seem unrelated to the bones, such as:
- Nasal congestion, uneven jaws or bulging eyes if bones in the face are affected
- Vision loss or hearing impairment if specific nerves become compressed due to the fibrous bone tissue
Monostotic Fibrous Dysplasia
- Diagnosed most often during the second and third decades of life.
- Males and females are affected with about equal frequency.
- Involved sites include the ribs, femur, and tibia, craniofacial bones, humerus.
- 70% to 85% of patients with fibrous dysplasia have disease limited to a single bone
- Maxilla is affected more often than the mandible.
Polyostotic Fibrous Dysplasia
- Involvement of two or more bones.
- Less common and more severe.
- Sites- femur, tibia ,pelvis ,ribs, skull ,facial bones, upper extremity, lumbar, cervical
- Age – before 10 years
- Sex- female> male
- The number of involved bones varies from a few to 75% of the entire skeleton.
Craniofacial Fibrous Dysplasia
- Bone disease of the face and skull that replaces normal bone with fibrous-type tissue.
- This 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
Dental Involvement
- Bones including the maxilla and mandible.
- Can cause massive expansion of the craniofacial complex.
- Severe malocclusion.
- Facial disfigurement lesions can grow rapidly, leading to bone expansion, and displacement of adjacent structures.
Lab Findings
No significant change in serum calcium/phosphorus Elevated Alkaline phosphatase Moderate increase in Basal Metabolic Rate.
Histopathologic Features
- Irregularly shaped trabeculae of immature (woven) bone in a cellular fibrous stroma.
- The lesional bone fuses with normal bone, without a capsule or line of demarcation.
- Abnormal bony trabeculae tend to be thin and disconnected, with curvilinear shapes likened to Chinese characters.
- Osteoblastic rimming is usually absent or minimal,
- Irregularly shaped trabeculae of woven bone in a fibrous stroma.
Radiological Features
Shepherd’s crook deformityRefers to a distinctive abnormal contour of the proximal femur in the setting of fibrous dysplasia. As the bone deforms the angle made between the neck of the femur and shaft of the bone.
Periapical radiograph showing a diffuse “ground-glass” radiographic appearance.
Syndromes Associated
McCune-Albright syndrome,
- characterized by polyostotic fibrous dysplasia,
- café au lait pigmentation,
- multiple endocrinopathies
Jaffe-Lichtenstein syndrome,
- characterized by polyostotic fibrous dysplasia
- café au lait (coffee with milk) pigmentation.
Mazabraud syndrome,
- characterized by fibrous dysplasia and intramuscular myxomas.
Treatment
- Conservative treatment-prevent deformity.
- Surgery-complete resection, restoring function &improving facial aesthetics
