It is a non hereditary, developmental anomaly of the bone due to defect in osteoblastic differentiation and maturation in which bone is replaced by fibrous tissue.
Etiology:
Exact cause is unknown.
However it is reported that postzygotic somatic mutation in GNAS1 (Guanine nucleotide-binding protein, a stimulating activity polypeptide) gene located at chromosome 20q13.2.
Etiopathogenesis:
GNAS1 gene encodes for G-protein which is involved in the production of cAMP in many tissues including endocrine function, melanocyte activity and osteoblast differentiation
↓
mutation in GNAS1 gene
↓
continuous activation of G-protein
↓
overproduction of cAMP
↓
Dysfunction of
1) Endocrine tissues causing:
a. Precocious puberty
b. hyperthyroidism
c. increased production of GH and cortisol
2) Melanocyte activity:
Cafe-au-lait spots with irregular margins unlike
neurofibromatosis.
3) Osteoblastic differentiation:
Medullary bone is replaced by fibrous tissue, which appears radiolucent on radiographs, with a classically described ground-glass appearance.
Clinical Features:
Two forms of fibrous dysplasia;
A. Polyostotic fibrous dysplasia:
- 20 to 30%
- involves more than one bone
- Sites: Femur, Tibia, Pelvis, Ribs, Skull and facial bones (in the decreasing order of their frequency)
Sign and symptoms:
1. Bone pain and fractures of extremities
2. Bowing of long bones
3. Curvature of the femoral neck and proximal shaft leads to characteristic "Shepherd Crook deformity" (pathognomonic)
4. Cutaneous pigmentation (50% patients) called "cafe au lait" spot is seen (macules)
5. Endocrine dysfunction
Notes:
MCCune-Albright syndrome:
Polyostotic fibrous dysplasia showing a tried of
1. Bone defects
2. Varying endocrine deformities and
3. Cafe-au-lait spots
Mazabraud syndrome:
Fibrous dysplasia with multiple intramuscular myxomas called Mazabraud syndrome.
B. Monostotic fibrous dysplasia:
- Common and less severe (70 to 80% patients)
- Sites: Ribs (28%), Femur (23%), tibia, craniofacial bones (10-25%) and humerus
- M = F, children
- When maxilla is involved, the patient gives typical leonine appearance (leontiasis ossea)
Oral manifestations:
2. Malalignment, tipping or displacement of the teeth (due to progressive expansile nature of lesion)
3.delayed eruption or altered eruption sequence and dislocation/malposition of teeth (due to loss of bone support and/or endocrine disturbances)
Radiographic features:
- appears as a radiolucent lesion in which normal trabecular pattern is completely lost and endosteal portion of bone may show scalloping.
- Rind sign
-Early lesions unilocular or multilocular radiolucencies
- Mature lesions: radiopaque spicules in the radiolucencies giving "ground glass" appearance or "orange peel" appearance.
the characteristic
Histologic features:
1.Numerous C-shaped trabeculae of woven bone, not connected to
each other and showing no relation to functional patterns
2. Bony trabeculae imparting the characteristic "Chinese letter pattern".
3. Low to moderate fibrous connective tissue in background
4. Fibrous connective tissue shows mononuclear cells resembling osteoblasts and fibroblast.
Differential Diagnosis:
1.Non-ossifying fibroma
2. Aneurysmal bone cyst
3. Fractured callus
4. Giant cell tumour
5. Low grade osteosarcoma
Treatment:
No specific treatment since it is self limiting and ceases to grow when patient reaches to puberty.
Treatment of monostotic fibrous dysplasia:
- cosmetic surgery
- Optic canal decompression therapy (to prevent from blindness)
- Vitamin D and Bisphosphonates therapy (to relieve bone pain and reduce osteoclastic activity)
Treatment of polyostotic fibrous dysplasia:
- Radiotherapy is not a choice ( chances of radiation induced sarcomas)
- address multiple bone defects and endocrine dysfunction
Prognosis: Good
Malignant Transformation incidence in
- Monostotic fibrous dysplasia 0.4%
- MCCune-Albright syndrome: 4%
Common malignancies reported are:
1. Osteosarcoma
2. Fibrosarcoma
3. Chondrosarcoma
4. Malignant fibrous histiocytoma
Common Viva Questions:
Q. What is ground glass appearance in case of fibrous dysplasia?
- Ground glass = Glass with smooth ground surface that renders it
non-transparent while retaining its transparency
Q. What are Cafe-au-lait spots?
- These are flat macules or pigmented birthmarks.
Q. Other conditions where Cafe-au-lait spots can be seen:
- 1. Neurofibromatosis
2. McCune-Albright syndrome
3. Fibrous dysplasia
Q. How Cafe-au-lait spots in fibrous dysplasia are differentiated from that of neurofibromatosis?
- Having irregular margins ( In neurofibromatosis they are regular outlined)
Q. What is McCune-Albright syndrome?
Polyostotic fibrous dysplasia showing a tried of
1. Bone defects
2. Varying endocrine deformities and
3. Cafe-au-lait spots
Q. What is Mazabraud syndrome?
- Fibrous dysplasia with multiple intramuscular myxomas called Mazabraud syndrome.
Q. What is rind sign in fibrous dysplasia?
- The translucent lesion has a thick sclerotic border and called rind sign
Some Common MCQS:
1. Fibrous dysplasia is the defect of:
a. Osteoblastic differentiation and maturation
b. Osteoclastic differentiation and maturation
c. Fibroblastic differentiation and maturation
d. All of the above
Correct answer is a.
2. Cafe-au-lait spots with irregular margins can be seen in
a. Neurofibromatosis
b. Fibrous dysplasia
c. Both of the above
d. None of the above
Correct answer is b.
3. Ground glass appearance is the characteristic feature of
a. Paget's disease
b. Osteopetrosis
c. Neurofibromatosis
d. Fibrous dysplasia
Correct answer is d.
4. Onion Peel appearance is the characteristic feature of
a. Paget's disease
b. Osteopetrosis
c. Neurofibromatosis
d. Fibrous dysplasia
Correct answer is d.
5. Shepherd Crook deformity is the characteristic presentation of
a. Paget's disease
b. Osteopetrosis
c. Neurofibromatosis
d. Fibrous dysplasia
Correct answer is d.
6. Most common extra skeletal manifestation of fibrous dysplasia is:
a. precocious puberty
b. Hyperthyroidism
c. Cafe-au-lait spots
d. Diabetes
Correct answer is c.
7. McCune-Albright syndrome is associated with
a. Monostotic fibrous dysplasia
b. Polyostotic fibrous dysplasia
c. Paget's disease
d. Osteopetrosis
Correct answer is b.
8. Age of onset of fibrous dysplasia is:
a. Below 10 years
b. 20 to 40 years
c. Above 60 years
d. None of the above
Correct answer is a.
9. Leontiasis ossea is seen in
a. Paget's disease
b. Osteopetrosis
c. Neurofibromatosis
d. Fibrous dysplasia
Correct answer is d.
10. Rind sign is the characteristic feature of
a. Paget's disease
b. Osteopetrosis
c. Neurofibromatosis
d. Fibrous dysplasia
Correct answer is d.
11. Chinese letter pattern is the feature of
a. Paget's disease
b. Osteopetrosis
c. Neurofibromatosis
d. Fibrous dysplasia
Correct answer is d.
