Introduction: Parathyroid carcinoma is a rare malignant tumor, accounting for less than 1% of primary hyperparathyroidism cases. It typically presents with severe hypercalcemia, very high PTH levels, and a large cervical mass. However, some atypical forms can complicate preoperative diagnosis.

Clinical Case: We report the case of a 44-year-old woman with no significant medical history, in whom a parathyroid incidentaloma was discovered during the investigation of neck pain. Phosphocalcic testing revealed a persistent elevation of PTH with normal serum calcium, confirming normocalcemic primary hyperparathyroidism after correction of a vitamin D deficiency. Localization imaging demonstrated a left parathyroid lesion. A parathyroidectomy was performed. Histopathological examination confirmed parathyroid carcinoma by immunohistochemistry. Due to persistent postoperative abnormalities, further surgery and staging were performed.

Conclusion: This case highlights that parathyroid carcinoma can present with subtle biological features without overt hypercalcemia. It underscores the importance of rigorous evaluation of normocalcemic hyperparathyroidism and the difficulty of preoperative diagnosis.