Coincident diabetes mellitus and primary hyperparathyroidism

The prevalence of diabetes mellitus in primary hyperparathyroidism is approximately 8% and that of primary hyperparathyroidism in diabetic patients is approximately 1%. Both values are about three-fold higher than the respective expected prevalences in general populations. Patients with both disorders are over 40 years of age and 80% are female; 22% have type 1 and 78% type 2 diabetes. Primary hyperparathyroidism presents first in approximately 20% of patients, and diabetes mellitus in 40%; both disorders present together, or within 1 year, in 40%. Approximately 40% of patients with primary hyperparathyroidism have impaired glucose tolerance. Insulin resistance is present in hyperparathyroidism and probably arises from a raised intracellular free calcium concentration which, by decreasing normal insulin-stimulated glucose transport, increases the requirement for insulin: if this insulin resistance progresses, impaired glucose tolerance and diabetes mellitus would result. Parathyroidectomy has been followed by regression of diabetes and of impaired glucose tolerance in some but not all patients. Early diagnosis of the second disorder is clinically desirable when one disorder is present. Hyperparathyroid patients should therefore be screened for impaired glucose tolerance and diabetes annually, and pre-operatively. Diabetic patients should be checked for hypercalcaemia at appropriate intervals; although only 1% of them may have hyperparathyroidism, this disorder if untreated is associated with hypertension, to which diabetic patients are already prone.