Tumor Induced Osteomalacia: A Case Report

Tumor-induced osteomalacia (TIO), also named Oncogenic Osteomalacia, is a rare paraneoplastic syndrome of renal phosphate wasting caused by a bone or soft tissue tumor. The tumor promotes overproduction of phosphatonin, a growth factor 23 (FGF23) that affects the proximal renal tubules, resulting in hypophosphatemia due to increased renal phosphate excretion, and osteomalacia. Symptoms include muscle weakness, fatigue and bone pain, as well as high risk of pathological fractures due to the osteomalacia.

This disorder puts a challenge in clinical diagnosis, which is often delayed and is eventually made with PET/SPECT scans to identify the location of the tumor. Treatment essentially involves resecting the tumor.

Case Report:
33 year old patient presented to the ER with back pain, began workup including MRI which demonstrated several thoracic compression fractures and AVN of femoral heads. Further investigation revealed low bone density and metabolic bone disease with hypophosphatemia, along with high FGF-23 levels. Bone scan and PET-DOTA scan were performed and demonstrated osteoclastic lesion in the 6th rib – assumed as TIO.

Using Video-Assisted Thoracoscopic Surgery (VATS) the patient underwent complete resection of the rib and the tumor. Pathology was compatible with Phosphaturic Mesenchymal tumor. Follow up – improvement of pain and levels of phosphate and FGF-23 levels.

Conclusion:
This rare disease puts a diagnostic challenge to the physician. As described in the literature, treatment involves resection and lead to cure, as demonstrated in this case report.