Occult phosphaturic mesenchymal tumour of femur cortex causing oncogenic osteomalacia - diagnostic challenges and clinical outcomes

Endokrynol Pol. 2018;69(2):205-210. doi: 10.5603/EP.a2018.0016. Epub 2018 Feb 14.


Background: Tumor induced osteomalacia (TIO) are extremely rare paraneoplastic syndrome with less than 300 reported cases. This report highlights the pitfalls and challenges in diagnosing and localizing TIO in patients with refractory and resistant osteomalacia.

Patient and methods: 41- year gentleman with 4-year history of musculoskeletal weakness and pathologic fractures presented in wheelchair bound incapacitated state of 1-year duration. Investigations were significant for severe hypophosphatemia, severe phosphaturia, normal serum calcium, reduced 1,25-dihydroxy vitamin-D, elevated ALP, elevated intact parathyroid hormone (iPTH), and pseudo-fractures involving pelvis and bilateral femur. Whole body MRI and 99mTc methylene diphosphonate bone-scan were also normal. Whole body FDG-PET scan involving all 4 limbs revealed a small FDG avid lesion at lateral border of lower end of left femur (SUV max 3.9), which was well characterized on 3-dimensional CT reconstruction. Plasma C-terminal fibroblast growth factor (FGF)-23 was 698 RU/ mL (normal < 150 RU/ml). Wide surgical excision of the tumor was done. Histopathology confirmed mesenchymal tumor of mixed connective tissue variant. Serum phosphorous normalized post-surgery day-1. High dose oral calcium and vitamin-D was continued. FGF-23 normalized post surgery (73RU/ml). Physical strength improved significantly and now he is able to walk independently.

Conclusion: TIO is frequently confused with normocalcemic hyperparathyroidism and vitamin-D resistant rickets/osteomalacia, which increases patient morbidity. Imaging for tumor localization should involve whole body from head to tip of digits, cause these tumors are notoriously small and frequently involve digits of hands and legs. Complete surgical removal of the localized tumor is key to good clinical outcomes.

Keywords: fibroblast growth factor; hypophosphataemic osteomalacia; paraneoplastic; phosphatonin; tumour induced osteomalacia.

Publication types

  • Case Reports

MeSH terms

  • Adult
  • Calcium / therapeutic use
  • Femur / diagnostic imaging
  • Femur / surgery
  • Fibroblast Growth Factor-23
  • Fibroblast Growth Factors / blood
  • Humans
  • Male
  • Neoplasms, Bone Tissue / complications*
  • Neoplasms, Bone Tissue / diagnosis
  • Neoplasms, Bone Tissue / diagnostic imaging
  • Neoplasms, Bone Tissue / surgery
  • Neoplasms, Connective Tissue / blood
  • Neoplasms, Connective Tissue / diagnosis
  • Neoplasms, Connective Tissue / drug therapy
  • Neoplasms, Connective Tissue / etiology*
  • Osteomalacia
  • Paraneoplastic Syndromes / blood
  • Paraneoplastic Syndromes / diagnosis
  • Paraneoplastic Syndromes / drug therapy
  • Paraneoplastic Syndromes / etiology
  • Vitamin D / therapeutic use


  • FGF23 protein, human
  • Vitamin D
  • Fibroblast Growth Factors
  • Fibroblast Growth Factor-23
  • Calcium

Supplementary concepts

  • Oncogenic osteomalacia