Endocrine Abstracts

Introduction

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused mainly by a phosphaturic mesenchymal tumour (PMT) as a consequence of fibroblast growth factor 23 (FGF23) overproduction. The manifestation of TIO is mostly musculoskeletal. Locating the PMT is usually challenging and a successful surgical resection of the tumour leads to complete recovery.

Case presentation

A 42-year-old, Caucasian male patient, moving with the help of crutches, was admitted to our Clinic in August 2018, for exacerbating muscle and joint pain, and waddling gait. The pain of the lumbar spine and both feet was noticed for the first time in May 2014. The neurological treatment with pregabalin, venlafaxine, methylprednisolone, physiotherapy, and high doses of antibiotics due to suspicion of borrelia infection were not helpful in pain relief. Laboratory results revealed hypophosphatemia, hyperphosphaturia, and a high level of alkaline phosphatase. A chest CT showed multiple fractures of spinous processes both sides of the rib cage. Based on the clinical manifestation and the additional examinations, including 68GaDOTA-TATE PET/CT performed in March 2018, PMT of the right femur was suspected. In May 2018, the tumour resection was performed and the histopathological examination of the lesion confirmed the diagnosis. However, the patient’s condition and post-surgical laboratory parameters had not improved. A second 68GaDOTA-TATE PET/CT scan revealed two lesions: in previously operated femoral bone and in jaw. After a systemic venous sampling of FGF23, performed to decide which foci should be treated, we focused on the right thigh. In January 2019, we carried out transarterial embolization (TAE) of the vessels supplying blood to the PMT to facilitate subsequent radiofrequency ablation (RFA) of the tumour remnants. After TAE and RFA, a profound improvement of the patient’s condition was observed and he was able to walk without the aid of crutches, and the waddling gait withdrew. However, despite FGF-23 normalization, he presented with severe hypophosphatemia, and a year after the RFA a fatigue fracture of the left tibia occurred. A third 68GaDOTA-TATE PET/CT, performed in July 2020, showed an increased expression of somatostatin receptors of the tumour remnants. Treatment with somatostatin analogs turned out to be ineffective. In December 2020, a successful surgical resection of the PMT combined with prophylactic intramedullary nailing of the femur resulted in phosphates normalization and complete recovery.

Conclusion

By presenting this case we would like to encourage clinicians to persist in locating PMT and therefore resection, which may require innovative diagnostic tools and treatment.