A Case of Tumor-Induced Osteomalacia Detected by Venous Sampling

Abstract

Tumor-induced osteomalacia (TIO) can cause osteomalacia due to excessive production of fibroblast growth factor 23 (FGF23) by the tumor. Since TIO is a very rare disease, it is often misdiagnosed as intervertebral disc herniation, spondyloarthritis, or osteoporosis. We report a 65-year-old man who developed generalized arthralgia and difficulty walking two years ago and was diagnosed with multiple fractures throughout his body. He was initially diagnosed with osteoporosis and was treated with calcitriol. However, he was referred to our hospital since his symptoms did not improve. We diagnosed tumor-induced osteomalacia based on low serum phosphorus, high bone-type alkaline phosphatase, high FGF23 levels, and the presence of two tumors. The responsible tumor was identified using FGF23 levels in venous sampling. As the location of the tumor made surgical resection difficult, we selected treatment with burosumab, a human monoclonal antibody against FGF23, leading to improvement in the hypophosphatemia and pain, such that he was able to walk with a cane. In cases of osteoporosis with hypophosphatemia, general physicians should keep TIO in mind, and attempt to identify the responsible tumor lesion.

Keywords:

• hypophosphatemia
• TIO
• FGF23
• burosumab

Data Sharing Statement

The datasets used during the current study are available from the corresponding author on reasonable request.

Ethics Statement

Based on the regulations of the Oita University Faculty of Medicine, institutional review board approval is not required for case reports.

Consent for Publication

Written informed consent was obtained from the patient for publication of this case report and any accompanying images.

Acknowledgments

We would like to express our sincere gratitude to Dr. Nobuaki Ito of the Department of Nephrology and Endocrinology, Faculty of Medicine, The University of Tokyo, for his cooperation in performing the venous sampling.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors have no competing interests to declare.

Additional information

Funding

There is no funding to report.