Hypercalcemic Crisis in A Patient with A Huge Mediastinal Atypical Parathyroid Adenoma

ABSTRACT Objective: To describe a patient who presented with hypercalcemic crisis and severe hyperparathyroidism who had urgent surgery. She was found to have a huge mediastinal atypical parathyroid adenoma (APA). We discuss our case, the difficulty discriminating an APA from parathyroid cancer, and the tools that help differentiate these conditions. Methods: We present the clinical manifestations, laboratory results, radiologic and surgical findings, and management in a patient with hyperparathyroid crisis. Discussion follows. Results: We report a case of a 39-year-old woman who presented with symptoms of severe hypercalcemia. Her intact parathyroid hormone level was found to be markedly elevated, consistent with primary hyperparathyroidism. Imaging revealed an anterior mediastinal mass, suggestive of possible ectopic parathyroid tissue. Urgent surgery and subsequent pathologic study of the excised mass revealed a supernumerary 37.5-g parathyroid gland within the mediastinum surrounded by a rim of thymic tissue. Histologically, the adenoma did not meet the World Health Organization criteria for the diagnosis of parathyroid carcinoma; however, the adenoma had atypical pathologic features given an abnormal mitotic figure. Parafibromin staining was performed and largely negative in the center of the tumor. Germline analysis of the MEN1 and CDC73 genes revealed no pathogenic variants. Her postoperative course was complicated by hypocalcemia but took several days to develop. Conclusion: The distinction between APA and parathyroid carcinoma may be difficult, and parafibromin staining and genetic testing for CDC73 mutations should be considered, as the results have implications for patient follow-up as well as for patients' relatives. Abbreviations: APA a typical parathyroid adenoma PHPT primary hyperparathyroidism PTH parathyroid hormone