FIBROUS DYSPLASIA: CLINICAL, RADIOGRAPHIC FEATURES & TREATMENT
Author: Sanketh DS, MDS
Fibrous dysplasia is a tumor like developmental condition, characterized by proliferation of abnormal cellular fibrous connective tissue with irregular trabecular bone replacing the normal medullary bone. This condition occurs due to a mutation in the GNAS (Guanine nucleotide-binding protein,α stimulating activity polypeptide) gene, encoding for the α subunit of G protein. Fibrous dysplasia affects/involves one bone (monostotic) or multiple bones(polyostotic), sometimes together with endocrine abnormalities and abnormal pigmentation.
Depending on the number of bones affected, fibrous dysplasia is classified as
1. Monostotic fibrous dysplasia if only one bone is affected.
2. Polyostotic fibrous dysplasia if multiple bones are affected.
3. Cranio-facial fibrous dysplasia if maxilla and its adjacent bones like zygoma, sphenoid,ethmoid, frontal, temporal, occiput are affected.
MONOSTOTIC AND CRANIO-FACIAL FIBROUS DYSPLASIA
This type accounts for 70-80 % of the condition and is common in children and young adults usually diagnosed during the 2nd – 3rd decades of life. There is an equal gender predilection and common sites involved are craniofacial bones, ribs, femur and tibia.
When it occurs on the jaws, it more often occurs on the maxilla than the mandible, frequently in the posterior regions. Mandibular lesions may be truly monostotic but maxilla is often affected along with multiple adjacent bones and is usually of the cranio-facial type.
A painless and a slow growing unilateral swelling of the jaw is usually the first clinical sign. The swelling involves the buccal or the labial surface and seldom the lingual plate. The inferior border may show an expansion sometimes, when the mandible is involved. The teeth may show displacement, mal-alignment and the eruption pattern may be disturbed. This lesion is diffuse, not well circumscribed and may produce a gross facial asymmetry.
Craniofacial involvement may cause vision changes, hypertelorism, facial deformity, exophthalmos, blindness, hearing defects and airway obstruction.
POLYOSTOTIC FIBROUS DYSPLASIA
A minor population of the patients exhibit involvement of more than one bone. This type is often diagnosed in patients lesser than ten years and has a female predilection. Upto 75% of the entire skeleton may sometimes be affected.
This type very often involves the skull and facial bones, spine, pelvis and shoulder girdle. Signs and symptoms start off with pain in the involved bone with spontaneous fracture. Limping, leg length discrepancy and bowing deformities are also seen.
A subset of the population affected with the polyostotic form of the disease may be associated with
1. Jaffe-Lichenstein syndrome: Polyostotic FD with café-au-lait pigmentation.
2. Mc-Cune Albright syndrome: Polyostotic FD, café-au lait pigmentation and multiple endocrinopathies.
3. Mazabraud syndrome: FD and intramuscular myxomas.
Café- au- lait pigmentation is in the form of hyperpigmented macules affecting the skin. These macules are irregular (resembling the coast of Maine) as opposed to the smooth regular macules in neurofibromatosis( like the coast of California).
Endocrine abnormalities are most often in the form of early puberty, particularly in females. They may exhibit menstrual bleeding, breast development and pubic hair in the first few years of life. Other endocrinopathies include hyperthyroidism, hyper-parathyroidism, acromegaly, hyper-cortisolism.
RADIOGRAPHIC FEATURES (JAW)
Appearances may range from being radiolucent to radio-opaque. Classically, it often manifests in the form of a “ground-glass” appearance also called as “peau d’orange” appearance. However this is not pathognomonic of fibrous dysplasia and it may also manifest as a unilocular or multilocular radiolucencies and a mottled radiolucent and radiopaque appearance (mixed). An additional “thumb-print” appearance has also been described. A characteristic feature of polyostotic FD is the “shepherd’s crook” deformity or the “hockey stick” deformity, where there is a malformation of the proximal femur.
Lesions of the jaw may show a buccal, bucco-lingual expansion and expansion of the inferior border of the mandible. There may be narrowing of the periodontal ligament space and ill defined lamina dura surrounding the teeth. Maxillary lesions may show displacement of the sinus floor.
Most cases of fibrous dysplasia stop growing after skeletal maturation and rare cases have shown regression. Patients who may have esthetic and functional problems may need surgical contouring, shaving and other debulking procedures.
Approximately 20-50% of the patients have shown re-growth after surgery, hence it is advised not to intervene till the condition has become quiescent. Along with surgery, orthodontic corrections and surgery could be done to correct malocclusion. Bisphosphonates have been shown to decrease pain occurring in this condition.
Radiation therapy is strictly contraindicated due to post radiation sarcomatous changes. There is a 1 % chance reported for malignant transformation to osteosarcoma and fibrosarcoma, in these patients especially patients with polyostotic changes and Mc-Cune Albright syndrome.
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