Fibrodysplasia

Fibrodysplasia: Description, Causes and Risk Factors:Fibrodysplasia is a common benign skeletal lesion that may involve one bone (monostotic) or multiple bones (polyostotic) and occurs throughout the skeleton with a predilection for the long bones, ribs, and craniofacial bones.FibrodysplasiaFibrodysplasia is postulated to occur as a result of a developmental failure in the remodeling of primitive bone to mature lamellar bone and a failure of the bone to realign in response to mechanical stress. Failure of maturation leaves a mass of immature isolated trabeculae enmeshed in dysplastic fibrous tissue that are turning over constantly but never (or very, very slowly) completing the re-modeling process. In addition, the immature matrix does not mineralize normally. The combination of a lack of stress alignment and insufficient mineralization results in substantial loss of mechanical strength, leading to the development of pain, deformity, and pathologic fractures.The etiology has been linked with a mutation in the Gs ? gene that occurs after fertilization in somatic cells and is located at chromosome 20q13.2-13.3. All cells that derive from the mutated cells manifest the dysplastic features. The clinical presentation varies depending on where in the cell mass the mutation is located and the size of the cell mass during embryogenesis when the mutation occurs. Severe disease may be associated with an earlier mutational event that leads to a larger number or a more widespread distribution of mutant cells. The sporadic occurrence of these diseases and the characteristic lateralized pattern of skin and bone involvement in the polyostotic forms of fibrodysplasia suggest this mosaic distribution of abnormal cells. The Gs ? gene has also been linked to other endocrine tumors and human diseases.The pathogenesis of fibrodysplasia involves somatic activating mutation of the gene encoding the alpha subunit of the stimulatory G protein (Gs ?) in the bone marrow cells, resulting in locally increased stimulatory activity of adenyl cyclase and cAMP. This mutation leads to increased production of C-fos protein and interleukin-6 (IL-6) that result in classic dysplastic bone of fibrodysplasia. The associated endocrinopathies are the result of constitutive activation of G protein coupled receptor by hormones acting through it including luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid stimulating hormone (TSH) and growth hormone-releasing hormone (GHRH) thereby manifesting as gonadotropin-independent precocious puberty (GIPP), hyperthyroidism and acromegaly respectively.There is no gender predilection for fibrodysplasia but it is more common in children and adolescents as compared to adults and older patients.Symptoms:The most common presenting manifestations are bone pains, deformity and fractures and sometimes isolated endocrinopathies like GIPP, thyrotoxicosis and acrogigantism. Bone deformity and facial asymmetry were common. Usually patients with monostotic fibrodysplasia have delayed presentation unless accompanied with endocrinopathies as compared to polyostotic variants. Other symptoms include thyroid gland problems and skin discoloration.Diagnosis:The diagnosis of fibrodysplasia is based on classical radiological findings substantiated by bone scans and characteristic pathological findings on histopathology. In some cases, your doctor may order more tests to confirm the diagnosis or to determine the extent of the disorder. They include:Imaging tests. Computerized tomography (CT) or magnetic resonance imaging (MRI) scans may be used to determine how extensively your bones are affected.
  • Bone scan. This test uses radioactive tracers, which are injected into your body. Your bones take up the tracers and emit radiation that's captured by a special camera, which produces a picture of your skeleton. Your doctor may order a bone scan to determine whether your fibrodysplasia is monostotic or polyostotic.
  • Bone biopsy. This test uses a hollow needle to remove a small piece of the affected bone for laboratory analysis. You'll receive local anesthetics to numb the area where the needle is inserted. In rare instances, an open biopsy — requiring general anesthesia and a surgical incision — may be necessary.
Treatment:Till recently, the treatment of fibrodysplasia was only restricted to symptomatic orthopedic management like correction of fractures, internal fixation, curettage and grafting. The use of bisphosphonate (intravenous pamidronate) in fibrodysplasia showed promising results with remarkable improvement in bone pain and healing of bone lesions. Similar effects were later shown by oral alendronate and intravenous zoledronate. The possible mechanism of action of bisphosphonates in fibrodysplasia is related to suppressed osteoclastic activation which occurs in fibrodysplasia due to constitutive activation of Gs ? subunit in the bone tissue.NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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