A Patient With Femoral Osteitis Fibrosa Cystica Due To Hyperparathyroidism: A Case Report

Background: Osteitis brosa cystica is a rare benign, lytic bone lesion attributed to hyperparathyroidism. The high level of parathyroid hormone cause rapid bone loss. Case presentation: The patient is a 50-year-old male complaining of severe sustained pain of the right knee joint. Imaging studies were suspicious for a benign tumor of the right distal femur. Biopsy under CT guidance showed numerous osteoclast aggregation and hemosiderin deposition around the bone trabeculae. Blood tests disclosed signicantly elevated parathyroid hormone, serum calcium, serum alkaline phosphatase. Parathyroid ultrasonography and CT scan showed a solid mass in front of the trachea at the thoracic entrance plane. After resection of the mass, the clinical symptoms were relieved and the radiological ndings were signicantly improved, which further conrmed the diagnosis. Conclusions: Metabolic diseases-associated bone lesions require a comprehensive diagnosis of multiple inspection items.An interprofessional team approach to the diagnosis and treatment of Osteitis brosa cystica will provide the best outcome.

The osteoclast activation in OFC is due to increased endogenous parathyroid hormone (PTH) [2].
Hyperparathyroidism is a common endocrine disorder characterized by elevated blood concentration of parathyroid hormone (PTH) and hypercalcemia, usually due to a benign adenoma. Primary or secondary hyperparathyroidism is often asymptomatic, however, severe forms may be diagnosed by lesions of target organs such as the skeletal system and the kidneys. Among patients with hyperparathyroidism, about 20% develop kidney stone disease [3]. Osteitis brosa cystica can occur as solitary or multiple lesions in any bone, most often in the mandible, pelvis, ribs and long bones [4,5]. The most typical skeletal manifestation of hyperparathyroidism were loss of cortical bone and trabecular remodeling due to osteoclast activation. OFC can be associated clinically with bone fractures, skeletal deformities and bone pain [6]. At present, osteitis brosa cystica, though rare, was easily misdiagnosed. We report a case of primary parathyroid adenom with OFC that presented clinically and radiologically as an aggressive metabolic bone disease.

Case Presentation
A 50 years old male presented to our institution for pain in the right knee joint. The pain gets worse during exercise and relieved at rest. Physical examination was unremarkable. CT scan showed cyst-like bone lesion at the distal part of femur with destruction of bone cortices, soap bubble like inner structure, sclerotic rim and no periosteal reaction (Fig. 1). Other CT scans showed kidney stones in this patient (Fig. 2). Contrast-enhanced magnetic resonance imaging of the knee joint showed a heterogeneous enhancement and clear boundary (Fig. 1). There was no soft tissue mass around the lesion. Biochemical blood tests revealed high calcium concentration (3.63 mmol/L, normal values 2.11-2.52 mmol/L) and low phosphorus concentration (0.5 mmol/L, normal values 0.85-1.51 mmol/L). The result tended to be a lytic bone tumor. A bone biopsy was performed under CT scan guidance, the sample was sent for histopathologic examination. Histopathological examination showed bone lesion composed of remodeled bone trabeculae with scattered groups of multinucleate giant cells of the osteoclast type with areas of hemorrhage and hemosiderosis. There was no evidence of malignancy in the biopsy sample (Fig. 3).
In order to verify hypercalcemia caused by hyperparathyroidism, parathyroid ultrasound and parathormone (PTH) were also performed. The concentration of PTH in serum is elevated (2034.6 pg/mL, normal values 12.0-88.0 pg/mL). Parathyroid ultrasound revealed a 3.6 × 1.6 cm solid mass in front of the trachea at the thoracic entrance plane. Contrast-enhanced CT scan of the parathyroid neoplasms showed heterogeneous enhancement and clear boundary (Fig. 2). Combined with the above results, we considered that bone lesion was related to parathyroid neoplasms.
After resection of the parathyroid adenoma, the patient no longer complained from knee joint pain and imaging performed six months later showed signi cant improvement, with reduction of the bone lesion dimensions and complete reconstruction of bone cortices (Fig. 4).

Discussion And Conclusion
Osteitis brosa cystica (OFC) is a disorder involving the bone which is resulted from excessive production of parathyroid hormone (PTH) due to hyperparathyroidism. Hyperparathyroidism might be due to parathyroid adenoma (up to 85% of cases), parathyroid hyperplasia, parathyroid carcinoma and hereditary factors [7]. As for the imageological diagnosis, CT showed cyst-like bone destruction, monocystic or polycystic, clear boundary and no periosteal reaction.The MRI examined no soft tissue mass formation around OFC which is a relatively characteristic phenomenon. OFC also often coexist with subperiosteal bone cortical resorption, subchondral bone resorption. Based on imaging manifestations, OFC needs to be identi ed from giant cell tumor of bone, aneurysm-like bone cysts, plasmacytomas. Pathological manifestations of the lesions surface is brown, formed by different size of the cysts. The cystic wall is brous tissue. When necrosis or hemorrhage occured in the cystic cavity, large numbers of multinucleated macrophages and hemosiderin-rich phagocytes appeared. Osteoclasts showed a sheet-like distribution. Inhomogeneous cancellous bone trabeculae was surrounded by osteoblasts.
The diagnosis of OFC may be challenging. In clinical practice, patient's symptoms are due to bone softening and hypercalcemia, which might include bone mass or fractures, kidney stones, peptic ulcer, weight loss, nausea and loss of appetite. However, these symptoms lack the speci city. In addition to the histological and radiological ndings, biochemical tests including PTH, serum calcium, alkaline phosphatase are also very important to ensure a correct OFC diagnosis.Treatment of osteitis brosa cystica starts with the management of hyperparathyroidism, such as parathyroid adenoma resection. After parathyroid adenoma resection, the majority of bone disorders resulting from OFC will resolve.
In summary, in current practice, skeletal manifestations of hyperparathyroidism are less common than in the past. OFC as a kind of metabolic diseases-associated bone lesion is easily misdiagnosed as bone tumor according to radiological and pathological characteristics. Serum calcium and PTH should be conventionally checked in patients with suspected metabolic bone disease. Elevated PTH levels and hypercalcemia are indicative of this disease and complement the radiological and histological features to con rm the diagnosis. If treated properly, OFC is reversible.

Declarations
The authors declare that data supporting the ndings of this study are available within the article.

Declarations
Ethics approval and consent to participate Medical Ethics Committee of Jingzhou Center Hospital has approved the research. The patient agreed to participate in this study and a signed consent form was obtained from the patient prior to the study. All procedures were conducted according to the Declaration of Helsinki.

Consent for publication
Written informed consent has been obtained from the patient for publication of this case report and any accompanying images.