Oncogenic osteomalacia caused by a phosphaturic mesenchymal tumor of the femur: A case report

BACKGROUND Oncogenic osteomalacia caused by phosphaturic mesenchymal tumors is very difficult to detect.We report a case of tumor-induced osteomalacia caused by a phosphaturic mesenchymal tumor of the left femur in a middle-aged woman after medical imaging and biopsy.CASE SUMMARY A 57-year-old woman presented with progressive bone pain for five years.She was diagnosed with hypophosphatemic osteomalacia,as her laboratory data showed low serum phosphorus and low serum calcium.Her knee joint radiography revealed an osteolytic lesion of the left femur.A computed tomography scan showed mixed density shadows in the left femur.Magnetic resonance imaging of the left femur showed the presence of an oval area with a hypointense signal in T1-weighted magnetic resonance imaging(MRI)and highlow mixed signal in T2-weighted MRI.Biopsy samples revealed the presence of short spindle cells,vascularization,and characteristics of phosphaturic mesenchymal tumors.Tumor resection was performed,and the clinical presentations and laboratory abnormalities were reversed.CONCLUSION Diagnosis of oncogenic osteomalacia is difficult due to the varieties and localization of source tumors and absence of pathognomonic biomedical signs.Our case highlights the importance of a combination of medical imaging and biopsy in the diagnosis of oncogenic osteomalacia caused by a phosphaturic mesenchymal tumor.

Oncogenic Osteomalacia Associated with Phosphaturic Mesenchymal Tumor of the Knee: Case Presentation and Review of the Literature

Oncogenic osteomalacia (OOM) is an uncommon metabolic and bone disease caused by fibroblast growth factor 23 (FGF23), a phosphaturic factor produced by phosphaturic mesenchymal tumors (mixed connective tissue variant, PMTMCTV) characterized by phosphate leakage from kidneys and subsequent hypophosphatemia. In this paper, we present the case of a patient, 42-year-old woman affected by left side limp and pain involving lumbar spine, pelvis and hip joints, referred to the Rheumatology Department of our Hospital for the treatment of a suspected sero-negative spondilo-arthritis. During hospitalization patient began an immuno-suppressive therapy with TNF-alpha inhibitors associated with Pamidornate, Indometacin, Esomeprazole and vitamin D3. Nevertheless pain did not decrease and a new examination found a worst hypophosphatemia (1 mg/dl) with normal Ca and PTH’s plasma values. During the same check-up a painful bulge on the anterior part of the right knee was observed and the Magnetic Resonance Imaging scan revealed an ovular solid lesion in the soft tissue closed to the upper part of the patella. Histological analysis identified the lesion as a PMTMCTV. After surgical removal patient got complete recovery. We will discuss about diagnostic evaluation, differential diagnosis and treatment.

Adult-onset hypophosphatemic osteomalacia as a cause of widespread musculoskeletal pain:A retrospective case series of single center experience

BACKGROUND Osteomalacia(OM)is frequently confused with various musculoskeletal or other rheumatic diseases,especially in patients with adult-onset widespread musculoskeletal pain because of its low prevalence and non-specific manifestations.AIM To facilitate the early diagnosis and etiology-specific treatment of adult-onset hypophosphatemic OM.METHODS A retrospective review of medical records was performed to screen adult patients who visited a physiatry locomotive medicine clinic(spine and musculoskeletal pain clinic)primarily presenting with widespread musculoskeletal pain at a single tertiary hospital between January 2011 and December 2019.We enrolled patients with hypophosphatemia,high serum bone-specific alkaline phosphatase levels,and at least one imaging finding suggestive of OM.RESULTS Eight patients with adult-onset hypophosphatemic OM were included.The back was the most common site of pain.Proximal dominant symmetric muscle weakness was observed in more than half of the patients.Bone scintigraphy was the most useful imaging modality for diagnosing OM because radiotracer uptake in OM showed characteristic patterns.Six patients were diagnosed with adefovir(ADV)-induced Fanconi syndrome,and the other two patients were diagnosed with tumor-induced OM and light-chain nephropathy,respectively.After phosphorus and vitamin D supplementation and treatment for the underlying etiologies,improvements in pain,muscle strength,and gait were observed in all patients.CONCLUSION Mechanical pain characteristics,hypophosphatemia,and distinctive bone scintigraphy patterns are the initial diagnostic indicators of adult-onset hypophosphatemic OM.ADV-induced Fanconi syndrome is the most common etiology of hypophosphatemic OM in hepatitis B virus-endemic countries.