Acral Mesenchymal Tumor Leading to Tumor-Induced Osteomalacia: Case Report and Literature Review

Abstract

Objective/Background

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by excessive secretion of fibroblast growth factor 23 (FGF-23) by phosphaturic mesenchymal tumors. This leads to hypophosphatemia, vitamin D deficiency, and impaired bone metabolism. TIO is often misdiagnosed due to its rarity and nonspecific symptoms.

Case Report

We report a 58-year-old male presenting with multiple nontraumatic fractures, muscle weakness, and functional decline. Laboratory evaluation revealed hypophosphatemia, elevated parathyroid hormone, reduced 1,25-dihydroxyvitamin D, and markedly elevated FGF-23 levels. Imaging identified a soft tissue mass in the plantar region of the right foot, which was confirmed as a phosphaturic mesenchymal tumor upon pathological analysis. The patient underwent surgical resection, resulting in rapid normalization of biochemical abnormalities, including serum phosphorus, parathyroid hormone, and 1,25-dihydroxyvitamin D, within 5 days.

Discussion

This case underscores the importance of recognizing TIO in patients with unexplained hypophosphatemia and fractures. The curative potential of tumor resection was demonstrated with rapid biochemical and clinical improvement. Diagnostic challenges often arise due to the rarity and atypical presentation of these tumors, particularly in uncommon locations such as the plantar region. Emerging therapies, such as FGF-23 inhibitors like burosumab, provide alternatives for nonlocalizable or unresectable tumors.

Conclusion

This case emphasizes the need for increased clinician awareness, multidisciplinary approaches, and advances in diagnostic imaging to reduce delays in diagnosing TIO. Further research is necessary to elucidate the pathophysiology, explore genetic associations, and improve treatment options for this debilitating condition.