Ninety-five percent of PHPT cases are sporadic. Of these cases, 75–85% result from a single adenoma, 2–12% result from double adenomas, 10–15% result from multiple gland hyperplasia, and <1% result from parathyroid carcinoma.
Patients with multigland disease tend to have PTH levels of <100 pg/mL, a negative preoperative localization, or several neurocognitive symptoms. Serum calcium levels of >14 mg/dL (3.5 mmol/L) or a palpable neck mass with elevated PTH may indicate parathyroid carcinoma . Familial endocrine disorders occur in approximately 5% of PHPT cases and frequently present in younger populations with a positive family history of neuroendocrine tumors or hypercalcemia.