Insulin resistance is not coupled with defective insulin secretion in primary hyperparathyroidism.

ABSTRACT

AIMS: An increased frequency of both impaired glucose tolerance and Type 2 diabetes mellitus (DM) has been reported in primary hyperparathyroidism (pHPT), thus we sought to investigate insulin sensitivity and insulin secretion in a large series of pHPT patients. SUBJECTS AND METHODS: One hundred and twenty-two consecutive pHPT patients without known DM were investigated [age (mean +/- sd) 59.3 +/- 13.6 years, body mass index (BMI) 25.7 +/- 4.2 kg/m(2); serum calcium 2.8 +/- 0.25 mmol/l; PTH 203.2 +/- 145.4 ng/l]. Sixty-one control subjects were matched, according to the degree of glucose tolerance, in a 2 1 patientcontrol ratio. Fasting- and oral glucose tolerance test-derived estimates of insulin sensitivity and secretion were determined by means of the quantitative insulin sensitivity check index (QUICKI) and the insulin sensitivity index (ISI) composite. RESULTS: Both the QUICKI and ISI composite were lower in pHPT patients than control subjects (P < 0.03 and P < 0.05, respectively) after adjusting for age, systolic blood pressure and BMI. Conversely, all insulin secretion estimates were significantly increased in pHPT patients than in control subjects (P < 0.04 and P < 0.03, respectively) and after adjusting for age, systolic blood pressure and BMI. Log serum calcium levels were negatively associated with the QUICKI and log ISI composite (R = -0.30, P = 0.001; R = -0.23, P = 0.020, respectively) in pHPT patients. Serum calcium levels significantly and independently contributed to impaired insulin sensitivity in multivariate analysis (QUICKI as dependent variable beta = -0.31, P = 0.004, R(2) = 0.15; log ISI composite as dependent variable beta = -0.29, P = 0.005, R(2) = 0.16). CONCLUSIONS: Our study confirms a reduction in both basal and stimulated insulin sensitivity in primary hyperparathyroidism, in spite of increased insulin secretion. Moreover, our data show for the first time a significant relationship between hypercalcaemia and insulin sensitivity in this condition.