A Striking Finding during Intraoperative Jugular Vein Sampling in a Case of Parathyroid Adenoma with Low-Normal Serum Intact Parathyroid Hormone Levels

Abstract

Aim: Primary hyperparathyroidism (PHP) is the most common cause of hypercalcemia based on outpatient clinic. The diagnosis of PHP is generally straightforward with high intact parathyroid hormone (iPTH) and hypercalcemia. But, PHP does not always exhibit those biochemical features. Less known phenotype of PHP is the hypercalcemia with normal level of iPTH. We report a case of parathyroid adenoma with low normal peripheral iPTH and high jugular PTH levels presenting as hypercalcemia. Our aim was to discuss the different mechanisms of such an entity with the guidance of the literature. Case: A thirty-six year old woman who has type 2 diabetes mellitus was admitted to the hospital with the diagnosis of acute pancreatitis. On laboratory examination serum calcium and iPTH levels were as follows: 10.6, 10.7, 10.9 mg/dL and 28.8, 33.3, 31.7 pg/mL, respectively. Twenty-four hour calcium excretion was 403 mg/day; serum phosphor was 2.3 mg/dL. Based on the findings of hypercalcemia, hypercalciuria, positive sonographic and scintigraphic images, operation was performed with the possible diagnosis of PHP. PTH measurement was taken from the right jugular vein. Intraoperative PTH was 634 pg/mL. Histopathological examination revealed as parathyroid adenoma. Postoperative hypocalcemia didn’t occur and postoperative calcium and iPTH levels were normal. Conclusion: Clinicians should be aware of the presence of low-normal iPTH in PHP. If the clinical suspicion of PHP is high as in our case, surgery should be performed after exclusion of other causes of hypercalcemia.