Ectopic Atypical Parathyroid Neoplasm in a Patient With Multiple Endocrine Neoplasia Type I

Objective: Present a case of an atypical parathyroid adenoma in the mediastinum as a part of multiple endocrine neoplasia type 1 (MEN1).Methods: Clinical, laboratory, imaging, and histolopathogic analyses were performed.Results: A 50-year-old man who was diagnosed with chronic kidney disease secondary to bilateral nephrolithiasis was referred for evaluation of incidentally detected hypercalcemia. He had an acromegaloid facies and lipomas over the forehead. Laboratory evaluation revealed hypercalcemia (3.33 mmol/L), hyperphosphatemia, and elevated intact parathyroid hormone level (215 pmol/L). Serum insulin-like growth factor 1 was elevated and growth hormone was non-suppressible on oral glucose load. Contrast-enhanced magnetic resonance imaging of the sella showed a pituitary microadenoma. A scan using 99mTc-Sestamibi and combined positron emission and computed tomography using fluorocholine F-18 revealed a mediastinal ectopic parathyroid adenoma, thereby attributing hypercalcemia to primary hyperparathyroidism. A clinical diagnosis of MEN1 was made. Genetic analysis revealed an A>T substitution at cDNA 253 in exon 2 of the MEN1 gene. He underwent median sternotomy and a 3 × 3-cm mass was excised, weighing 14 g. Histopathology showed parathyroid tissue with moderate pleomorphism, pushing margins, fibrous trabeculae, atypical mitoses, and low Ki-67 index, suggestive of atypical parathyroid neoplasm. After surgery the patient became normocalcemic. On follow-up, he is asymptomatic without any evidence of recurrence of primary hyperparathyroidism.Conclusion: Parathyroid involvement in MEN1 is almost exclusively in the form of benign hyperplasia. Atypical parathyroid adenomas and parathyroid carcinomas in MEN1 are very rare, limited to only a few anecdotal case reports to which ours contributes a new case.Abbreviations: CKD = chronic kidney disease;iPTH = intact parathyroid hormone;MEN1 = multiple endocrine neoplasia type 1