VOLUME 6 - NUMBER 1 - 2026

Parathyroidectomy for tertiary hyperparathyroidism related to tumor-induced osteomalacia (TIO)

  • Francesco Tonelli, Francesca Giusti, Francesca Marini, Maria Luisa Brandi
  • Case report, 46-56
  • Full text PDF

  • Rare mesenchymal tumors secreting fibroblast growth factor 23, a hormone with phosphaturic properties, can cause hypophosphatemia, hypercalcemia, and hyperparathyroidism (HPT), and be responsible for tumor-induced osteomalacia (TIO). When the tumor is not identified, or is not resectable, daily phosphate supplementation and calcitriol administration are recommended. Treatment is usually initiated with sodium phosphate 500 mg/twice daily and calcitriol 5 mg/day. Monitoring of serum and urinary biomarkers is essential for adjusting pharmacological doses.

    We report the case of a patient with TIO but no identified primary tumor, who, despite taking phosphate and calcitriol continuously for over 17 years, developed TIO-related tertiary HPT. Parathyroidectomy was necessary. During surgery, two hyperplastic parathyroid glands were excised, with intraoperative monitoring of circulating parathyroid hormone (PTH) decline. Postoperatively, calcium levels returned to normal, and PTH levels slightly increased.

    When TIO is diagnosed, laboratory monitoring every 3–6 months is recommended to adjust phosphate supplementation and prevent increased PTH secretion and the development of secondary HPT. If secondary HPT does develop, cinacalcet may be used to maintain normal serum calcium levels. In the presence of tertiary HPT, the extent of parathyroidectomy should be carefully evaluated to correct the HPT without causing hypoparathyroidism.

  • KEY WORDS: Hyperparathyroidism, tumor-induced osteomalacia, parathyroidectomy, fibroblast growth factor 23 (FGF23).