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Beitragstitel Osteopenia resistant to therapy: phosphaturic mesenchymal tumor as a rare cause
Beitragscode P65
Autoren
  1. Jan Danek Kantonsspital Uri Vortragender
  2. Carlo Theus-Steinmann Articon Spezialpraxis für Gelenkchirurgie
  3. Bruno Fuchs Luzerner Kantonsspital & Swiss Sarcoma Network
Präsentationsform Poster
Themengebiete
  • A07 - Spezialgebiet 3 | Tumore
Abstract Introduction
Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm of bone and/or soft tissue origins. This often solitary tumor ectopically secretes a bone cell–derived protein, fibroblast growth factor 23 (FGF23) which is responsible for the phosphate homeostasis. The high blood levels of FGF23 causes a renal phosphate wasting, hyperphosphaturia, leading to hypophosphatemia and hypovitaminosis D. The compensatory mobilization of calcium and phosphate from bones manifests clinically as widespread osteomalacia which maximally can lead to pathological fractures. Due to the presentation of a non-specific symptoms, the correct diagnosis is often delayed. The search for the origin of osteopenia can be frustrating. For PMT specifically, a 68-Gallium Dotatate PET CT tracer uptake represents a useful imaging.

Methods
We report a case of a 44-year-old man with more than a year history of progressive immobilizing back pain and acute shoulder and feet pain. Laboratory blood results showed hypophosphatemia (0,33 mmol/l), high bone-specific alkaline phosphatase (43,1 µg/l) and high levels of FGF23 (243 kRU/I). X-Ray and MRI revealed diffuse osteopenia, older sacral fracture and bone edema in femoral neck, no trauma in the past was reported. Before the PMT was diagnosed, attempts to manage osteomalacia with vitamin D and phosphate supplementation were consequently useless. The PET CT showed a 2.5 x 1.3 cm highly Dotatate and contrast binding tumor between left M. adductor magnus and M. adductor brevis. The core needle biopsy confirmed the suspected diagnosis of PMT.

Results
The patient then underwent a surgical resection. Thereafter, we noted a sharply decreased level of FGF23 (28 kRU/I) in the serum, associated with an improved phosphatemia (0,97 mmol/l), normalization of Vitamin D level (69 nmol/l) and a complete relief of systemic pain.

Conclusion
The diagnosis of PMT can be delayed even for years due to rarity, the non-specific symptoms and the failure to test serum phosphorus levels. The possibility of measurement of serum level of FGF23 in case of hypophosphatemic osteomalacia resistant to supplementation is a straightforward diagnostic way. To localize the tumor, a 68Ga-DOTATATE PET/CT scan is enormous helpful. A core needle biopsy confirms the suspicion. Complete surgical removal of the PMT is the treatment of choice and results in the resolution of the osteomalacia, blood abnormalities and pain.