A Herald of Plasma Cell Myeloma: A Report of Malignant Plasma Cells Identified in Parathyroid Adenoma and a Review of Non-parathyroid Malignancies in Parathyroid Glands.

Involvement of the parathyroid glands by non-parathyroid neoplasia is an infrequent event. Rare cases of metastases to the parathyroid gland have been reported in parathyroidectomies and autopsies of patients with known solid or hematopoietic malignancies. Here, we present a case of atypical clonal plasma cells incidentally identified within a parathyroid adenoma resected for hyperparathyroidism and hypercalcemia, which served as the sentinel event for a subsequent diagnosis of plasma cell myeloma. To our knowledge, this is the only reported case of a hematopoietic malignancy involving a parathyroid adenoma and the only reported case of malignant hematopoietic cells initially detected in parathyroidectomy.