Fibrous Dysplasia

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Information about Fibrous Dysplasia

Published on April 3, 2016

Author: drpuls


1. Fibrous Dysplasia DEFINITION EPIDEMIOLOGY CLASSIFICATIONS PRESENTATION NATURAL HISTORY MACROSCOPIC APPEARANCE / HISTOLOGY DIFFERENTIAL DIAGNOSIS TREATMENT COMPLICATIONS DEFINITION Benign condition in which normal lamellar bone is replaced by fibrous connective tissue due to a defect in osteoblast differentiation and maturation, resulting in formation of bone that is weak and prone to expansion. EPIDEMIOLOGY Incidence not known Females > Males No race predilection Initial symptoms manifest age 3-15yrs Not heritable Questionable genetic transformation Malignant transformation in < 1% GENETIC BASIS – GNAS1 mutation, early mutation leads to diffuse disease whereas late mutation leads to isolated disease. CLASSIFICATIONS Fibrous Dysplasia can affect any bone and can be divided into four subtypes (although there is some overlap): 1. Monostotic : single bone 2. Polyostotic : multiple bones 3. Craniofacial Fibrous Dysplasia : skull and facial bones alone 4. Cherubism : mandible and maxilla alone (not true fibrous dysplasia, Cherubism is inherited as an Autosomal Dominant, with Histological features indistinguishable from a giant Cell Granuloma. Another Classification states it into 3 types : 1. Monostotic (70 percent)

2. 2. Polyostotic (25-30 percent) 3. McCune-Albright Syndrome MONOSTOTIC Most common (70%) No gender predilection Often quiesces at puberty 25% involve head and neck Most common sites: femur, tibia, ribs, skull POLYOSTOTIC 25% of cases 2 or more bones Female predilection 50% have head and neck involvement Less likely to become inactive McCUNE-ALBRIGHT SYNDROME 3% Multiple bony lesions Hyperpigmentation -- Café au lait spots Endocrine dysfunction – hyperthyroidism – precocious puberty in females It can also be classified Radiologically as – 1. Cystic (21%) – Radiolucency surrounded by solid rim 2. Sclerotic (23%) – Dense and homogenous 3. Pagetoid or Mixed (56%) – “Ground glass appearance” PRESENTATION Local pain (Pressure Symptom, initially no pain) Swelling Abnormal pigmentation Cranial Nerve compression Spontaneous scalp hemorrhage Part of McCune-Albright’s syndrome The most involved skull bones are Ethmoid (71 %) and Sphenoid (43 %). Frontal & maxillary bones can be involved in 30 % of the cases, while temporal and occipital bones are less likely to be affected, i.e. in 24 % and 5 %, respectively In Head and Neck > 95 cases reported involving temporal bone leading to – Conductive Hearing Loss (80%) – Narrowing of the EAC.

3. – Middle ear, ossicular or Eustachian tube CN VII paralysis – Erosion of Fallopian Canal SNHL, vertigo – Erosion of Otic Capsule Rarely Secondary Cholesteatoma. NATURAL HISTORY Structurally weak bones Elevated Alkaline Phosphatase – 30%, more common in Polyostotic Calcium and phosphorus normal Malignant degeneration – 0.4% – Osteosarcoma – Radiation increases risk by 400X – Monostotic, craniofacial – Signs: rapid growth, pain, elevated alkaline phosphatase MACROSCOPIC APPEARANCE Macroscopically lesions are intramedullary, well circumscribed with abnormal whitish-grey colour. HISTOLOGY Fibrous component Osseous component: resembles immature (woven) bone Arises metaplastically from lamellar bone Irregular, poorly-oriented trabeculae Lack osteoblastic rimming Cartilaginous islands present in 10% (differentiating feature from chondrosarcoma) DIFFERENTIAL DIAGNOSIS 1. Ossifying fibroma 2. Paget’s disease 3. Aneurysmal bone cyst 4. Giant cell tumor 5. “Brown tumor” Fibrous Dysplasia Ossifying Fibroma Developmental anomaly True benign neoplasm with capsule Onset – < 25 yrs of age 25 years of age Size – usually > 4cm Usually < 4cm in size Slight gender predilection F:M – 8:1 25 – 50 percent seen in head and neck 90 percent in mandible MANAGEMENT

4. Investigation of choice remains CT scan. MRI can also be done but not as specific as CT. At the initial presentation, Radionuclide Bone Scintigraphy is useful to demonstrate the extent of the disease The isotope scan shows increased uptake throughout life, but the uptake becomes less intense as the lesions mature. Bone scintigraphy is sensitive for detecting lesions, but the tracer uptake is nonspecific. Expectant management – Observation Conservative – Surgical Excision/Shaving Radical – Resection for cure A patient with preserved vision and acceptable or minimal cosmetic deformity may be a candidate for serial clinical and radiological observation. Acute changes heralded by the sudden onset of diplopia, pain, or changes in visual function must be seriously considered and may represent coexisting disease such as cystic changes or the presence of hemorrhage or mucoceles. In these cases in which disease is clearly correlated with acute symptoms, expedient surgical intervention may be warranted. Medications, such as bisphosphonates, calcitonin, and mithramycin, targeted at reducing bone resorption/osteoclastic activity have been prescribed based on the premise that increased osteoclastic activity is seen with fibrous dysplasia Intravenous bisphosphonates may be helpful for treatment of bone pain, but there is no clear evidence that they strengthen bone lesions or prevent fractures. Managing endocrinopathies is a critical component of management in FD. All patients with fibrous dysplasia should be evaluated and treated for endocrine diseases associated with McCune–Albright syndrome. In particular untreated growth hormone excess may worsen craniofacial fibrous dysplasia and increase the risk of blindness. Corticosteroid agents have also been used in the care of patients with fibrous dysplasia. Systemic corticosteroids have been used successfully as a temporizing measure in patients with acute visual loss. Radiation contraindicated as increased risk of malignant transformation. COMPLICATIONS Pathological Fracture. Bone Deformity. Massive Cartilage Hyperplasia. Accelerated bone growth. Sarcomatous changes.

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