Case report: incidental parathyroid adenoma in a Chinese diabetic patient with hypercalcemia and normal parathyroid hormone levels.

Rationale: Parathyroid hormone PTH) levels are the main parameters to differentiate primary hyperparathyroidism (PHPT) from non-PTH-dependent hypercalcemia. We report a case of hypercalcemia with normal PTH levels due to a parathyroid adenoma.

Patient Concerns: A 52-year-old female patient presented with 2-year history of documented sustained high-normal serum calcium and hypercalcemia (2.51-3.03 mmol/L) with normal serum intact PTH levels (21.95-40.15 pg/ mL).

Diagnoses: A parathyroid tumor was localized by ultrasonography and 99mTc-sestamibi dual-phase fusion imaging with single-photon emission computed tomography/computed tomography.

Interventions: Parathyroidectomy was performed to excise the tumor completely.

Outcomes: A 1.2-cm-sized parathyroid adenoma was removed surgically. The serum calcium was declined to normal level immediately after resection, as well as in 4- month follow-ups. The immunohistological diagnosis proved to be a PTH positive parathyroid adenoma.

Lessons: In case of hypercalcemia, serum intact PTH and parathyroid imaging should be monitored to evaluate the presence of parathyroid adenoma with care because PHPT could present with inappropriate normal PTH.