Fibrous dysplasia of bone

Fibrous dysplasia of bone is a non-heritable disease in which abnormal tissue grows bone instead. The etiology of this process of growth is correlated with abnormal mutation in a gene that encodes the subunit of stimulatory G protein located on chromosome 20. As a consequence of this mutation, there is a subtitutie the histidine-cysteine ​​amino acids of genomic DNA from osteoblast cells with another amino acid-arginine. Because these substitutions Osteoblasts elaborate fibrous tissue in bone marrow instead of normal bone tissue.
Abnormalities may involve a bone-shaped monostotic (70% of cases) or more bones in the polyostotic form (30% of cases).Polyostotic form is occasionally associated with precocious puberty, fibrous dysplasia and café-au-lait lesions (Albright syndrome) or skeletal muscle myxomas (Mazabraud syndrome).
In fibrous dysplasia lesions are characterized by deposition of fibrous tissue in the bone and bone marrow fibrosis. Mechanical quality of bone is diminished. As a result of this fragile bone fracture patients at increased risk. The incidence of fractures is 50%. The risk of fracturing a bone or bone deformity is higher in long bones such as femur, tibia and humerus, but all bones can be affected. Pain is a common symptom of patients with fibrous dysplasia. Patients may be at high risk of malignant transformation: osteosarcoma, fibrosarcoma, chondrosarcoma and malignant fibrohistiocitom. Incidence risk was assessed at 1%. This risk is higher in patients with McCune-Albright syndrome or polyostotic form.
Fibrous dysplasia is about 5% of benign bone tumors. Monostotic form is more common than the polyostotic. Many patients are asymptomatic, so the true incidence of the disease is unknown.The disease usually presents in children and adolescents, with an average age of onset of 8 years. Most cases occur before age 30 years. Men are affected more often than women, except Albright syndrome in which women are affected more often than men.
Fibrous dysplasia require surgical treatment to prevent or treat major deformities or fractures. Is the most common surgical indication for a bone fracture or participating in support affect progress in body weight. Asymptomatic patients require no treatment. It will make the needle biopsy if there is doubt about the diagnosis before surgery. Upper extremity injuries often require surgery. Some studies show the usefulness of bisphosphonates in relieving chronic pain in patients with fibrous dysplasia.
Fibrous dysplasia appellant has been reported in 21% after curettage and grafting, but patients should be monitored for several years and the recurrence rate increases to 100%. If you do not develop malignant transformation, fibrous dysplasia is not a life threatening disease. Lesions tend to stabilize when skeletal maturity is reached. Most cases have a good evolution monostotic regardless of treatment. Polyostotic lesions are frequently associated with fractures.
Pathogenesis and causesFibrous dysplasia is caused by sporadic mutation of a gene that encodes the alpha subunit of stimulatory G protein located on chromosome 20 osteoblasts. The consequence of this mutation is in abnormal cell differentiation dexorganizarea bone matrix.Maintaining normal bone structure is disturbed, and suffers bone physiological changes and is replaced by abnormal fibrous tissue proliferation. Extending the model depend on the stage of disease development and Loctite the mutation occurs. All bones can be affected.These forms of the disease are recognized:Forma monostotic-Form of polyostoticCraniofacial-shape-Heruvismul.
Signs and symptomsThe disease is about 5% of benign bone tumors. Monostotic form is more common than the polyostotic. Many patients are asymptomatic, so the true incidence of the disease is unknown.The disease usually presents in children and adolescents, with an average age of onset of 8 years. Most cases occur before age 30 years. Men are affected more often than women, except Albright syndrome in which women are affected more often than men.
Pain is a common sign of fibrous dysplasia in symptomatic patients. Most often patients are asymptomatic. Patients seek professional help because of painful swelling and deformation of bones and pathological fractures due to a weakened bone. Long bones are most commonly affected. Femur is the most common location. Other sites are the tibia, jaw and skull.Nonscheletice manifestations include abnormal skin pigmentation, precocious puberty, hyperthyroidism, Cushing disease, hyperparathyroidism and hypophosphatemia rahistismul. Albright syndrome is defined as a triad consisting of precocious puberty, polyostotic fibrous dysplasia and cutaneous pigmentation.Typically only women are affected by precocious puberty, but other endocrine disorders occur equally in men and women. All these anomalies are considered to be due to the same mutations.
Monostotic form of bone dysplasia:Approximately 80% of cases of disease are monostotic. This form affects mostly ribs, femur, tibia and craniofacial bones, humerus, vertebrae, in descending order of frequency. It presents with pain or pathologic fractures in patients with ages between 10-70 years, but especially those between 10-30 years. The degree of bone deformity is less severe than in the polyostotic form. There are no data to clearly confirm monostotic conversion to the polyostotic form.
The form of polyostotic bone dysplasia:Approximately 30% are polyostotic fibrous dysplasia. Most commonly affects the skull and facial bones, pelvis, spine and shoulders. Dysplasia is unilateral or bilateral and affects several bones of the same State with or without axial skeletal involvement.Although polyostotic activity tends to produce unilateral distribution, and generalized asymmetric involvement occurs when the disease is bilateral.
Form craniofacial bone dysplasia:This pattern of damage occurs in 25% of patients with an monostotic and 50% of those with polyostotic form. Appears as isolated craniofacial form. In isolated form extracranial injuries are present. Occipital and temporal bones are rarely affected.Hypertelorism, cranial asymmetry, facial deformation, visual impairment, exophthalmos and blindness are due to periorbital bone damage. Sphenoid and temporal impairment cause vestibular dysfunction, tinnitus and deafness. When damage occurs resulting hyposmia or anosmia cribriform plate.
Heruvismul:This special variant of fibrous dysplasia is an autosomal dominant disorder with variable penetrance. Occurs in children and especially boys. Regression can occur after adolescence. The lower jaw is large and protrudes. Damage is symmetrical jaw and mandible.
Complications fibrodisplaziei BoneFracture is the most common complication of fibrous dysplasia. In polyostotic disease, fracture occurs in more than 50% of cases.Deformation may occur in bones that support weight. Malignant transformation occurs in less than 0. 5% of cases. Polyostotic disease is more common in or after radiotherapy. Typically occur in the third or fourth decade of life. Albright syndrome, shows the high incidence of scoliosis.The rate of scoliosis in patients with polyostotic fibrous dysplasia is 45%. Most spinal lesions are located in the lumbar or thoracic region, few lesions are located at the sacrum or neck. Posterior spinal elements are involved in 70% of cases.Sexual precocity in girls, with polyostotic fibrous dysplasia and McCune-Albright syndrome is skin blemishes.Extrascheletica skin pigmentation is the most common manifestation. Occurs in 50% of patients with polyostotic form. It is ipsilateral to the localization of the lesion, differentiating it from neurofibromatosis pigmentation disease. Spots are associated with an increased amount of melanin in basal cells of epidermis.They tend to be linear or segmental arranged near the midline of the body, the lumbar spine, sacrum and buttocks, neck and shoulders. Similar lesions appear on the lips and mucous membranes. Pigmentation can occur at birth and precedes the development of skeletal and endocrine abnormalities.
Evolution fibrodisplaziei BoneIf you do not develop malignant transformation, fibrous dysplasia is not a life threatening disease. Lesions tend to stabilize when skeletal maturity is reached. Most cases have a good evolution monostotic regardless of treatment. Polyostotic lesions are frequently associated with fractures. Recurrence of lesions is 100% in the coming years.