[Diabetes mellitus and carbohydrate metabolism in primary hyperparathyroidism]

It is generally known that patients with primary hyperparathyroidism (pHPT) feature disturbances in carbohydrate metabolism and hypertension. The incidence and prevalence of frank diabetes mellitus is significantly increased in these patients. The etiology and pathogenesis of the vascular and metabolic aberrations in this condition are still unclear. Glucose intolerance in pHPT is characterized by severe insulin resistance associated with pancreatic beta cell hypersecretion of insulin. Hypercalcemia is thought to be mainly responsible for the impaired glucose metabolism. However, several studies demonstrated that hypophosphatemia can also induce insulin hypersecretion and impair peripheral glucose uptake. Hypertension in primary hyperparathyroidism is mainly attributed to hypercalcemia. However, high peripheral insulin levels are also proposed to contribute to the development of essential hypertension and hyperinsulinemia per se is regarded as an important independent cardiovascular risk factor. After parathyroidectomy and decrease of the calcium levels to within the normal range, the blood pressure levels of the patients with pHPT normalised very quickly, whereas normalization of the high peripheral insulin levels was only found in a subgroup of patients. Thus, hypercalcemia seems to be mainly responsible for hypertension in primary hyperparathyroidism. Another important, yet unresolved issue is the question as to whether or to which extent the disturbances in glucose homeostasis are reversible after surgical correction of pHPT. At an early stage of the disease, insulin resistance and insulin hypersecretion are fully reversible after parathyroidectomy, whereas in patients with long-standing primary hyperparathyroidism and severely impaired glucose tolerance the metabolic disturbances will only partially improve. These results argue for improved screening to identify asymptomatic patients with primary hyperparathyroidism and for early surgical intervention in this disease.