Introduction: Primary hyperparathyroidism is usually caused by a parathyroid adenoma (80-85%), occasionally by primary parathyroid hyperplasia (10-15%), and rarely by atypical parathyroid tumor (APT) or carcinoma (<1%). APT reflects parathyroid neoplasm of uncertain malignant potential which poses a challenge for differential diagnosis with parathyroid carcinomas. Most patients exhibit strong symptomatology of hypercalcemia at presentation shared with the benign causes of hyperparathyroidism. We present a rare case of atypical parathyroid tumor who presented with hypercalcemia and end organ damage.
Case Report: 33-year-old gentleman was referred to our endocrine service in 2021 for optimal management of primary hyperparathyroidism following admission for with adjusted calcium 3.29 mmol/l(2.2-2.6). Calcium reduced to 2.98 mmol/lwith intravenous fluids. He had symptomatic hypercalcemia with muscle weakness over several years leading to a fall where he had spontaneous right patella tendon rupture requiring repair in 2011 and left patella tendon repair in 2012. Clinically there were no suggestive features of syndromic hyperparathyroidism and no significant family history. He was clubbed and had muscle wasting in both lower limbs. Biochemistries revealed that serum calcium was 3.33 mmol/l, PTH was 54.7 pmol/l(1.6-6.9), phosphate was 0.52 mmol/lwhich were in keeping with primary hyperparathyroidism. Bone densitometry and renal ultrasound scans demonstrated osteoporosis and nephrolithiasis respectively. Parathyroid ultrasound scan showed a heterogeneous cystic mass in the left side of the neck 25x30x41 mm suggestive of a degenerative parathyroid adenoma, although the 99m Tc-MIBI scan did not detect adenoma. A 4D-CT demonstrated an intra-thyroidal cyst but was unable to exclude this being a cystic parathyroid lesion. Cinacalcet commenced to control hypercalcemia prior to the surgery. Subsequently, he underwent the left parathyroidectomy. There was a clear plane between the thyroid and parathyroid adenoma despite the suggestion on imaging. Histology appearances are suggestive of atypical parathyroid tumour in the new WHO 2022 classification, Ki67 < 1%. Following postoperative care, his calcium and parathyroid hormone levels normalized. Genetic testing showed heterozygosity for a CDC73 variant of uncertain clinical significance. His family was counselled for further genetic testing.
Conclusion: This case highlights some of the complications patients can experience if there are delays in diagnosis and treatment of primary hyperparathyroidism. It also demonstrates the importance of genetic testing and the potential uncertainties this can yield for patients. APT is rare and no specific guidelines for the surveillance of patients with atypical parathyroid adenomas after parathyroid surgery exist so far.