Paraneoplastic Osteomalacia Secondary to a Pancreatic Neuroendocrine Tumor

Abstract

Introduction: Tumor-induced osteomalacia (TIO) is a rare condition, usually associated with mesenchymal tumors that produce fibroblast growth factor 23 (FGF23). Clinical case: We present the case of a 46-year-old man with diffuse bone pain, muscle weakness, progressive fatigue, and a pathological fracture. Laboratory studies revealed hypophosphatemia, hypocalcemia, vitamin D deficiency, elevated alkaline phosphatase, and increased parathyroid hormone levels. After excluding common secondary causes, imaging studies identified a nodular lesion in the pancreatic tail suggestive of a neuroendocrine tumor. The patient underwent a laparoscopic distal pancreatectomy with spleen preservation. Histopathological analysis confirmed a well-differentiated grade 2 neuroendocrine tumor. During postoperative follow-up, progressive normalization of serum calcium and phosphate levels was observed, along with significant improvement in bone mineral density. Discussion: This case supports the rarely documented possibility that a pancreatic neuroendocrine tumor can serve as a source of FGF23 and cause TIO, emphasizing the importance of considering this etiology in patients with unexplained osteomalacia.