Thyroid follicular adenoma producing parathyroid hormone-related protein with a normal serum calcium level.

A 64-year-old woman had normal serum calcium and plasma parathyroid hormone levels, despite an extremely high plasma parathyroid hormone-related protein (PTHrP) level. She underwent medical screening at our hospital and several neck tumors were detected by ultrasonography. After surgical resection of these tumors, her plasma PTHrP level was normalized. Histological examination showed that the resected tumors were thyroid follicular adenomas, while immunohistochemistry revealed positive staining with a monoclonal antibody for PTHrP. This is a rare case of thyroid follicular adenoma producing PTHrP in a patient with a normal serum calcium level despite elevation of plasma PTHrP.