Phosphaturic mesenchymal tumor: Case report

Osteolytic mystery: A rare case of pathologic fracture from a phosphaturic mesenchymal tumor in hip and femur

Phosphaturic mesenchymal tumor (PMT) is a rare tumor causing bone complications and myopathy. Histologically, PMT displays a mix of spindled cells, osteoclast-like giant cells, basophilic matrix, and flocculent or "grungy" calcification. Here we describe a case of PMT in the right hip and proximal femur, initially suspected to be multiple myeloma, presenting with osteolytic lesions and elevated alkaline phosphatase. Tests for malignancy were negative, but a subsequent biopsy confirmed PMT. The patient underwent hip biopsy, femur resection, and hemiarthroplasty, with follow-up MRI recommended.

A 50-Year-Old Man Presenting with Multiple Bone Lesions and a Diagnosis of Phosphaturic Mesenchymal Tumor of the Femur

BACKGROUND Phosphaturic mesenchymal tumor (PMT) is an extremely rare mesenchymal neoplasm that is commonly seen in bone and soft tissue. It is associated with a paraneoplastic syndrome, oncogenic osteomalacia, due to tumor-induced urinary phosphate wasting. It is demonstrated to be predominantly mediated by fibroblast growth factor 23 (FGF23)/fibroblast growth factor receptor 1 (FGFR1) axis. Clinically, PMT usually presents as a solitary lesion in the bone. The diagnosis of PMT is challenging due to its non-specific clinical manifestation, radiologic findings, and morphological features. CASE REPORT We report the case of a 50-year-old man presenting with multiple lytic bone lesions and associated pathologic fracture of the right femur, clinically suspicious for multiple myeloma or other metastatic malignant process. Resection from the right femur showed a hypercellular lesion composed of oval-to-spindled cells infiltrating the native trabecular bone with admixed multinucleated giant cells. Immunohistochemical (IHC) staining and in situ hybridization (ISH) demonstrated the tumor cells were positive for SATB2, ERG, FGFR1, and FGF23 ISH. DNA and RNA next-generation sequencing showed marked increases in mRNA levels of FGF23 and FGFR1. The constellation of clinicoradiologic, histomorphologic, IHC, and molecular findings supported a diagnosis of primary benign PMT. CONCLUSIONS This case report discusses a patient with PMT presenting with multifocal lesions due to tumor-induced osteomalacia at initial presentation. We hope that this report will increase the awareness of clinician and pathologists of PMT as a differential diagnosis in patients presenting with multifocal lytic bone lesions. In turn, this will prevent misdiagnosis and overtreatment of a typically benign process.

Tumor induced osteomalacia from a peripheral mesenchymal tumour of the foot

Tumour induced osteomalacia (TIO) is a rare condition caused by peripheral mesenchymal tumours (PMT) which produce fibroblast-growth factor 23 (FGF23). FGF23 inhibits renal phosphate reabsorption leading to vitamin D resistant osteomalacia. The rarity of the condition and difficulty with isolating the PMT make diagnosis difficult, with delayed treatment leading to significant patient morbidity. We present a case of PMT of the foot with TIO, with a discussion on diagnosis and treatment.

Phosphaturic Mesenchymal Tumor

Phosphaturic mesenchymal tumors (PMTs) are neoplasms associated with tumor-induced osteomalacia. Patients typically present with pathologic fractures in the setting of chronic hypophosphatemic hyperphosphaturic osteomalacia, as well as gradual muscle weakness, bone pain, and difficulty walking. Because of their rarity and nonspecific symptomatology, phosphaturic mesenchymal tumors often go undiagnosed for years. Even when discovered on imaging, the tumors can be diagnostically challenging for radiologists. Phosphaturic mesenchymal tumors often tend to be small and can be located nearly anywhere in the body, and, therefore, can mimic many other tumors. This case highlights the imaging and pathologic markers of a phosphaturic mesenchymal tumor, often found in a patient with tumor-induced osteomalacia.

Diagnosis and surgical treatment of tumor-induced osteomalacia—a literature review and a case report

Background

Tumor-induced osteomalacia (TIO) is a rare condition with fewer than 500 cases reported in the literature although described. Phosphaturic mesenchymal tumor (PMT) is often unrecognized cause of hypophosphatemia. This case report aims to highlight such a rare association which warrants clinical and radiologist attention.

Case

A 51-year-old man had pain in his feet 2 years prior to the most recent presentation in our clinic. The patient experienced increasingly severe body aches and pain, which affected the feet, hips, knees, ribs, waist, and shoulders. MRI and CT led to the diagnosis of multiple insufficiency fractures. Laboratory tests showed that inorganic phosphate (IP) levels had decreased to 0.52 mmol/L(0.81–1.45 mmol/L), while alkaline phosphatase (ALP) had increased to 216 U/L(38.0–126.0 U/L). Positron emission tomography computed tomography showed tumor-derived hypophosphate osteomalacia of the right iliac wing; surgical resection was performed. markers of bone metabolism and bone density returned normal postoperative, after 9 months follow-up.

Conclusion

The possibility of tumor-induced osteomalacia should be considered if unexplained joint pain, decreased bone mineral density, increased ALP and insufficiency fractures, and no similar family history are found in adult patients. Surgical resection of the tumor is the key to the treatment.

A Case of Femoral Neck Insufficiency Fracture due to Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare skeletal disease caused by hypersecretion of fibroblast growth factor 23 (FGF-23) from neoplasms of mesenchymal origin; patients with TIO present with insufficiency fractures, progressive bone pain, and delayed fracture unions. Herein, we report the case of a 48-year-old man with an insufficiency fracture in his left femoral neck associated with TIO. The causative tumor located in the patient's maxillary sinus had been resected; however, complete resection was impossible due to the location of the tumor. Therefore, the patient's osteomalacia persisted, and he experienced a left femoral neck fracture in the absence of severe trauma. Because delayed fracture union was anticipated in this patient, we performed an internal fixation using an implant with a lateral plate for angular stability and multiple screws for rotational stability. Although fracture union took 15 months, the patient's postoperative course was uneventful, and he could walk without any symptoms or assistance at his most recent follow-up 30 months after surgery. In TIO, hypersecretion of FGF-23 leads to increased renal excretion of phosphorus, increased bone resorption of calcium and phosphorus, decreased osteoblastic bone mineralization, and decreased gastrointestinal absorption of calcium and phosphorus, leading to insufficiency fractures and delayed fracture unions. Diagnosis of TIO is often delayed due to its rarity and vague symptoms. Total resection of the causative tumor is the optimal treatment; however, in cases wherein complete tumor resection is impossible, drug therapy may be insufficient, and the underlying TIO pathology, including bone fragility, may persist. Early diagnosis of TIO is important for preventing insufficiency fractures; however, when fractures are unavoidable, the surgical treatment of femoral neck fractures in patients with osteomalacia should account for a longer time frame for complete fracture union and therefore utilize implants with sufficient stability.