Polyostotic fibrous dysplasia in a 6-year-old boy

Fibrous dysplasia (FD) is a rare congenital benign bone disease, that is manifested as a defect in the bone remodeling process, affecting the function, differentiation and maturation of the osteoblasts. This process is located in the bone marrow, where the normal marrow tissue is being replaced with immature bone islands and fibrous stroma. The etiology is unclear so far, but it is known to be connected with a point mutation of the gene that encodes Gs α protein in the time of embryogenesis, and as result of that, all of the affected somatic cells become dysplastic. It is important whether the mutation occurred earlier in the process of embryogenesis, so that there will be more mutant cells and the disease will appear in a more severe form. The clinical presentation of FD is variable, so there are plenty of potential differential diagnosis. The most common include Paget disease, nonossifying fibroma, osteofibrous dysplasia, aneurysmal bone cyst, adamantinoma, giant cell tumor, fracture callus and low-grade central osteosarcoma