Objective: The clinical profile of asymptomatic primary hyperparathyroidism (PHPT) had shifted from a symptomatic disorder toward a more subtle, asymptomatic state. The lack of knowledge about the natural course of asymptomatic PHPT contributes to the controversy regarding the optimal management of these patients. The aim of this study is to evaluate the natural course of calcium and glucose metabolism abnormalities, insulin sensitivity, and bone mineral density (BMD) in subjects with asymptomatic PHPT over 18 months.

Design: The study was designed as a prospective observational examination of asymptomatic PHPT patients at baseline and at 6-month intervals for 18 months.

Methods: Our study examined 61 patients with asymptomatic PHPT and 80 healthy control subjects matched for age, sex, and body mass index. We evaluated calcium metabolism, glucose metabolism by oral glucose tolerance test, insulin sensitivity by homeostasis model assessment (HOMA) index, and BMD by dual energy x-ray absorptiometry at distal radius, lumbar spine, and femur.

Results: Although in asymptomatic PHPT patients HOMA index at baseline was slightly higher than in controls (3.0 ± 2.2 vs. 2.2 ± 1.3, P = 0.035), the prevalence of preexisting diabetes mellitus (DM) (13.1% vs. 11.3%), undiagnosed impaired fasting glucose (34.4% vs. 30%), impaired glucose tolerance (13.1% vs. 18.8%), and newly diagnosed DM (4.9% vs. 2.5%) were similar. Baseline BMDs (g/cm²) at all three sites were not different between two groups. Six-month interval measurements showed no change in calcium metabolism parameters including serum calcium, phosphorus, 25-hydroxyvitamin D, and 24-hour calcium excretion. No significant longitudinal adverse changes were noted in glucose metabolism, insulin sensitivity, or BMD at any site over the 18-month observation period.

Conclusions: Our follow-up of patients with asymptomatic PHPT revealed no progression of calcium and glucose metabolism abnormalities, insulin sensitivity, and loss of bone mineral density during the 18-month study period.