Endocrine Abstracts

Background: Primary hyperparathyroidism (PHPT) is nowadays an asymptomatic disease characterized by mild hypercalcemia and elevated parathormone (PTH) levels. A non-typical form of the disease distinguished by high PTH levels, normal serum calcium concentrations, and no evidence of secondary hyperparathyroidism was recently identified. The data about parathyroid imaging findings in the normocalcemic type of the disease are lacking. Ultrasonography (US) is the most convenient imaging modality for localization of parathyroid adenoma. The purpose of our study was to investigate whether normocalcemic patients harbor abnormal parathyroid glands on high-resolution ultrasonography.

Methods: We studied 14 patients (aged 53.2±10.3 years) with normocalcemic primary hyperparathyroidism. High-resolution ultrasonography was performed to locate parathyroid adenomas. Ten patients with positive sonography underwent a parathyroid ⁹⁹technetium sestamibi scintigraphy (MIBI).

The following variables were measured: serum total calcium, PTH, creatinine, phosphate, alkaline phosphatase, 25 hydroxyvitamin D and 1.25 dihydroxyvitamin D. A 24-hour urine collection was obtained for assessment of calcium and creatinine excretion rates. Corrected serum calcium level was used as an indirect assessment of ionized calcium.

The local Institutional Review Board approved the study, and all patients gave informed consent.

Results: All patients had high PTH levels (112±33.1 pg/ml), normal corrected serum calcium (9.6±0.3 mg/dl) and 25 hydroxyvitamin D (27.5±5.3 ng/ml) levels and normal creatinine clearance (97±18.6 ml/mn). Ten out of 14 patients (71%) exhibited a total of 12 single or double typical parathyroid adenomas on sonography. Sestamibi imaging correctly localized 8 of them.

Conclusion: The high prevalence of parathyroid adenomas on sonography indicates that normocalcemic primary hyperparathyroidism is characterized by the same morphologic derangement as the hypercalcemic form of the disease. Thus, NPHP is probably an early manifestation of PHPT.