Endocrine Abstracts

Introduction: Tumor-induced osteomalacia (TIO) or oncogenic hypophosphatemic osteomalacia (OHO) is a rare paraneoplastic syndrome characterized by renal phosphate wasting leading to hypophosphatemia and secondary osteomalacia. TIO was first described in 1947 by Robert McCance and only 500 of cases have been reported in literature since then, approximately 200 of cases during this decade.

Case report: In 2014, a 32-year-old female presented with waist pain, myalgia, muscle weakness. The patient felt unhealthy after second childbirth. In June 2015 MRI scan revealed bilateral acute sacroiliitis. Treatment with sulphasalazine, methylprednisolone, methotrexate and later with etanercept was started, but was ineffective. In May 2016 repeated MRI showed bilateral avascular femoral head necrosis of unknown origin. Plain radiography showed osteoporosis at thoracic, lumbar vertebrae, hip bone and femur, fracture of superior ramus of pubis, compressive fractures in Th8-Th9. Dual energy x ray absorptiometry (DXA) scans confirmed low bone mineral density at the spine 0.516 g/cm² (Z-score −4.8), hip neck 0.507 g/cm² (Z-score −2.9) and hip total 0.496 g/cm² (Z-score −3.6). Other causes of secondary osteoporosis were excluded and the antiosteoporotic treatment with denosumab was started. The patient was first seen by an endocrinologist in October 2016 because of progressing symptoms. Biochemical evaluation revealed hypophosphatemia 0.3 mmol/l (n: 0.78–0.153) and low 24-h urine phosphorus excretion 8.78 mmol/24 h (n: 12.9–42.0). Hypophosphatemia was treated with phosphate supplements but where was no improvement. In September 2017 patient noticed a soft lump in the right groin. Right leg ultrasound and MRI revealed 1.5×1.8×2.0 cm size tumor between sartorius and adductor longus muscles. Whole-body MRI and bone scintigraphy showed no metastasis or other tumors. In October 2017 the whole-body scintigraphy with somatostatin analogues 99mTC-tektrotyd showed intensive uptake of radiotracer at the tumor. Tumor biopsy was performed and the result confirmed giant cell tumor of soft tissue (GCT-ST). FGF-23 values were found increased eightfold and being 867 U/l (n: 26–110). With strong prediction of TIO, in January 2018 the patient underwent tumor removal surgery. One week after surgery serum phosphate reached normal range. Histopathology examination is still in process.

Conclusion: A stepwise approach to tumor localization with functional and anatomic imaging for the diagnosing TIO is essential. Patients should first be assessed with a thorough physical examination. Removal of the tumor successfully cures this debilitating disease.