Endocrine Abstracts

Background: Although primary hyperparathyroidism (PHPT) has been associated with diabetes mellitus (DM), the etiological link is not clear and the effect of parathyroidectomy is controversial.The aim of this observational study was to investigate the metabolic link between calciotropic hormones and glucose metabolism in PHPT patients before and after parathyroidectomy.

Methods: Twenty-four consecutive patients with PHPT (Group-A) without DM were included in the study. Anthropometric characteristics and medical history were recorded. Fasting plasma glucose (FPG), fasting insulin (FI), calcium, phosphorus, parathyroid hormone (PTH) and 25-hydroxyvitamin-D [25(OH)D] were measured. Homeostasis Model Assessment was used for estimating insulin resistance (HOMA-IR) and β-cell function (HOMA-B). QUICKI index for insulin sensitivity was also calculated. In a subgroup of 13 patients (Group-B) a scheduled curative parathyroidectomy was performed and all measurements were repeated after surgery. In 10 out of 13 a 75 g OGTT was performed before and 6 weeks after surgery to further evaluate glucose response, insulin response and insulin sensitivity using Matsuda Index. SPSS 22 was used for statistical analysis.

Results: Group-A had a mean age of 55±10.66 years and the female:male ratio was 19:5. Pearson and Spearman correlation coefficient was used and a statistically significant positive correlation between HOMA-B and PTH (r=0.53, P=0.008) was identified. PTH was also correlated to waist-to-hip ratio (r=0.44, P=0.03) and inversely to FPG/FI ratio (r=−0.40, P=0.056). Linear regression showed a significant linear relation between HOMA-B and PTH (P=0.006), which remained significant when adjusted for age and BMI.When subjects were classified according to their 25(OH)D levels in vitamin D sufficient [25(OH)D ≥20 ng/dl, n=16] and vitamin D insufficient (10<25(OH)D<20 ng/dl, n=8), independent samples t-test showed no significant difference in glucose homeostasis. In Group-B after surgery, calcium and PTH levels normalized and phosphorus increased. T-paired test and Wilcoxon signed rank test were used but no significant alterations were identified in FPG (P=0.56), FI (P=0.73), HOMA-IR (P=0.65), HOMA-B (P=0.53), QUICKI (P=0.90), Matsuda index (P=0.10), BMI (P=0.17).The correlation between HOMA-B and PTH remained significant after surgery (r=0.76, P=0.002).

Conclusion: Findings of this small study indicate a correlation independent of vitamin D between PTH and indices of β-cell function and insulin sensitivity, in PHPT patients. This parallel increase of HOMA-B and PTH could be due to insulin resistance or reflect a potential direct action of PTH on β-cell. Larger studies will clarify the mechanisms and explain the inability of parathyroidectomy to reverse this effect.