Elevated Intact Parathyroid Hormone Produced by a Cervical Neuroendocrine Tumor

ABSTRACT Objective To describe the diagnosis of a case of hypercalcemia secondary to elevated intact parathyroid hormone (iPTH) due to a cervical neuroendocrine tumor. Methods We present the clinical, laboratory, and imaging findings of the case, along with a review of the literature. Results A 69-year-old man with a history of bradypsychia, polyuria, and epigastric pain was hospitalized for hypercalcemia (13.7 mg/dL). The patient had elevated iPTH (326 pg/mL), suggesting primary hyperparathyroidism. An ultrasound and parathyroid single-photon emission computed tomography scan identified a possible left inferior parathyroid adenoma. The suspicious parathyroid lesion was surgically removed. The original mass was found to be normal but another tumor was found and identified as a solid, 5-cm infiltrating tumor which was not completely resected. Immunohistochemistry showed that the tumor was compatible with a neuroendocrine tumor, clearly positive for chromogranin and focally for iPTH. Postoperatively, his chromogranin A level was elevated (435 ng/mL). Scintigraphy with radiolabeled octreotide was positive in the cervical area without metastasis elsewhere. Calcemia and iPTH levels reduced sharply postoperatively, but began to rise after 1 month. Considering that resection was incomplete, chemotherapy was initiated along with cinacalcet and somatostatin analog administration, resulting in additional decrease in serum calcium levels (10.5 to 11 mg/dL) and disease stabilization. Conclusion This case highlighted a challenging diagnosis wherein an extra parathyroid tumor could produce ectopic iPTH. Biochemical and hormonal patterns compatible with primary hyperparathyroidism may not always be related to a parathyroid adenoma.