Fibrous dysplasia is a disease that causes aberrant development of osteoblasts, which results in fibrous stroma replacing normal bone. Lichtenstein first described it in 1938. It is a sporadic disorder caused due to a postzygotic mutation in the GNAS1 gene. It can affect a single bone (monostotic) or several bones (polyostotic). The most common locations are the skull & ribs. It is typically an incidental finding and asymptomatic. When a pathologic fracture or malignant alteration complicates it, symptoms could develop. As polyostotic FD is a rare disorder that only occasionally occurs in 20–25% of patients, therefore the aim of this article is to report such a rare case of polyostotic FD in a 30-year-old female patient showing the characteristic changes.
A developing benign medullary fibro-osseous condition known as fibrous dysplasia (FD) is characterised by the cessation of mature lamellar bone formation and the formation of woven bone, which may be multifocal.
A thirty-year old female patient presented with right hip discomfort and weight bearing difficulty after an episode of fall since the past 1 month. On local examination, right limb was externally rotated, swelling and tenderness was present in the middle 1/3rd of the thigh. Restricted range of movements of the hip joint was noted and active movements of ankle and toes were present. General physical examination was unremarkable. Vital signs were normal.
The first descriptions of the benign disorder fibrous dysplasia were made by Lichtenstein in 1938 and Jaffe in 1942.4 With 0.8% primary and 7% benign bone lesions, it is a rather rare disorder. In 70–80% of cases, it is monostotic, while in 20–30% of cases, it is polyostotic.
Diagnostic criteria according to WHO classification of soft tissue and bone tumors (5th edition):
A bone lesion with compatible imaging characteristics.
Osseous part consisting of irregular curvilinear branching trabeculae of woven bone without apparent osteoblastic rimming.
Fibrous part consisting of bland fibroblasts.
Evidence of GNAS activating missense mutations Imaging features include:
The appearance of fibrous dysplasia is usually smooth and homogeneous with endosteal scalloping and cortical thinning. There are clearly marked borders and the cortex is generally intact but thinned due to the expansive nature of the lesion. Other features include: ground-glass matrix, may be completely lucent (cystic) or sclerotic, well-circumscribed lesion with no periosteal reaction and in some cases rind sign, i.e. when a lesion is surrounded by a layer of thick, sclerotic reactive bone. In extremities, bowing deformities and shepherd crook deformity of the femoral neck might be seen.
Furthermore the above mentioned radiography findings, other findings like ground-glass opacities, homogeneously sclerotic lesion, cystic lesion, with well-defined borders can be seen.
Due to the numerous variations in how bone lesions look and the fact that they frequently resemble tumours or other more aggressive diseases. The ability of MRI to distinguish fibrous dysplasia from other conditions is not particularly useful. However, heterogenous signal intensity is seen on T1 and T2 weighted imaging with heterogenous post-contrast enhancement.
Through dietary changes and exercise, management attempts to gauge the severity of the condition and preserve bone quality. The prognosis is favourable and typically no more therapy is needed.
However, leg length disparities, deformities, and impingement or nerve compression disorders can all result from monostotic fibrous dysplasia.
Differential diagnosis of Paget’s disease and osteofibrous dysplasia should be ruled out.