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Updated: Jun 22 2021

Fibrous Dysplasia

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  • summary
    • Fibrous Dysplasia is a developmental abnormality caused by a GS alpha protein mutation that leads to failure of the production of normal lamellar bone.
    • The condition usually presents in patients who are less than 30 years of age with an asymptomatic lesion that is found incidentally on radiographs.
    • Diagnosis is made with radiographs showing a lesion with ground glass appearance or a "punched-out" lesion with a well-defined margin of sclerotic bone.
    • Treatment is usually nonoperative with bisphosphonates for pain control. Surgical management is indicated for lesions that lead to bone deformities such as scoliosis or coxa vara.
  • Epidemiology
    • Demographics
      • male:female ratio
        • females > males
      • age bracket
        • found in any and all ages
        • onset for 75% of patients at <30 years of age
    • Anatomic location
      • any bone can be involved
      • the proximal femur is most common site, followed by rib, maxilla, and tibia
  • Etiology
    • Genetics
      • associated with GNAS mutation
        • GS alpha protein (chromosome 20q13) activating mutation (affects cAMP signaling pathway leading to increased production of cAMP)
      • high production of FGF-23 which may lead to hypophosphatemia
    • Associated conditions
      • orthopedic manifestations
        • McCune Albright syndrome
          • condition defined by the presence of
            • skin abnormalities (cafe au lait spots in coast of Maine pattern)
            • endocrine abnormalities (precocious puberty)
              • renal phosphate wasting due to FGF-23 (oncogenic osteomalacia)
            • polyostotic fibrous dysplasia
              • obtain AP spine radiographs to look for scoliosis
        • Mazabraud syndrome
          • polyostotic fibrous dysplasia
          • soft-tissue intramuscular myxomas
        • Osteofibrous dysplasia
          • rare form that primarily affects the tibia and is confined to the cortices
      • nonorthopedic manifestations
        • severe cranial deformities with blindness
  • Presentation
    • Symptoms
      • usually asymptomatic and discovered as an incidental finding
      • may have swelling or deformity
      • bone lesions may be monostotic (80%) or polystotic (20%)
      • pain from stress fractures
    • Physical exam
      • inspection
        • cafe au lait spots
          • larger and more irregular borders ("coast of Maine") than neurofibromatosis
          • may or may not be present with fibrous dysplasia
          • by definition present with McCune-Albright syndrome
        • swelling around lesion
        • scoliosis
  • Imaging
    • Radiographs
      • hip/pelvis radiograph
        • central lytic lesions in medullary canal (diaphysis or metaphysis)
        • may have cortical thinning with expansile lesion
        • highly lytic lesions or a ground glass appearance
        • "punched-out" lesion with well-defined margin of sclerotic bone is common
        • modest expansion of bone
        • Shepherd's crook deformity
      • AP spine radiograph
        • vertebral collapse
        • kyphoscoliosis
    • Bone scan
      • usually warm
  • Studies
    • Gross - yellow-white gritty tissue
    • Histology
      • characteristic look of "alphabet soup" or "chinese letters"
      • fibroblast proliferation surrounding islands of woven bone
        • woven bone lacks osteoblastic rimming (osteofibrous dysplasia has osteoblastic rimming)
      • trabeculae of osteoid and bone in fibrous stroma with metaplastic cartilage or areas of cyst degeneration
      • mitotic figures are common
  • Treatment
    • Nonoperative
      • observation
        • indications
          • asymptomatic patients
      • bisphosphonate therapy
        • indications
          • symptomatic polyostotic fibrous dysplasia
        • effective in decreasing pain and reducing bone turnover
    • Operative
      • internal fixation and bone grafting
        • indications
          • symptomatic lesions
          • impending/actual fractures through lesions in areas of high stress (femoral neck)
          • severe deformity
          • neurologic compromise in the spine
        • technique
          • never use autogenous cancellous bone, as the transplanted bone will quickly turn into fibrous dysplastic woven bone
          • use cortical or cancellous allografts
          • intramedullary device more effective than a plate in the lower extremity
      • osteotomies
        • indications
          • coxa vara deformity
            • intertrochanteric osteotomy
  • Differential
      • Fibrous Dysplasia Differential 
      • Multiple lesions in young patients
      • Treatment is Observation alone
      • Benefits from Bisphonate therapy
      • Fibrous Dysplasia
      • o
      • o
      • o
      • Eosinophilic granuloma
      • o
      • o
      • Lymphoma
      • o
      • Leukemia
      • o
      • Enchondroma / Olliers / Maffucci's
      • o
      • o
      • Osteochondroma / MHE
      • o
      • o
      • NOF /Jaffe-Campanacci syndrome
      • o
      • o
      • Hemangioendothelioma
      • o
      • Paget's
      • o
      • o
      • Metastatic Disease
      • o
      • Myeloma
      • o
  • Prognosis
    • 1% risk of malignant transformation to osteosarcoma, fibrosarcoma, or malignant fibrous histiocytoma
      • poor prognosis
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