The improvement of insulin resistance in patients with adrenal incidentaloma by surgical resection

OBJECTIVE Several recent studies have indicated that patients with adrenal incidentaloma often have disturbed glucose tolerance or/and hypertension. It is unclear whether these metabolic conditions could be caused by adrenal incidentaloma. We investigated the prevalence of disturbed glucose tolerance, hypertension and insulin resistance in the patients with non-functioning adrenal incidentaloma and evaluated the changes of the parameters such as glucose tolerance, blood pressure and insulin sensitivity after adrenalectomy. PATIENTS AND METHODS Among 15 patients with incidentally discovered adrenal tumours in our department from 1996 to 1999, 4 patients were diagnosed as having pre-clinical Cushing's syndrome and the other 11 as having non-functioning tumours based on detailed endocrinological examinations including dexamethasone suppression testing. Four tumours with 'pre-clinical Cushing's syndrome and 8 tumours out of 11 patients with non-functioning tumours were diagnosed histopathologically as adrenocortical adenomas and the other 3 as of non-adrenal origin including a myelolipoma, an adrenal vascular cyst and an endothelioma. The prevalence of disturbed glucose tolerance was determined with an oral glucose tolerance test, and insulin sensitivity was evaluated by the method of steady state of plasma glucose (SSPG). RESULTS All 12 patients with adrenocortical adenoma exhibited insulin resistance based on the SSPG (6.9-13.2 mmol/l). Before surgical removal of the tumours, the SSPG titre was relatively higher in the patients with pre-clinical Cushing's syndrome than in those with non-functioning with adrenocortical adenoma (mean value 11.65 vs. 8.99 mmol/l), whereas 2 of the 3 patients with non-adrenocortical tumours did not have insulin resistance. Among the 12 patients with adrenocortical adenoma, 7 (58%) and 9 (75%) patients exhibited hypertension and disturbed glucose tolerance, respectively. After removal of the tumours, SSPG of the patients with adrenocortical adenoma, but not that of the other 3 patients with non-cortical tumours, was significantly decreased compared to pre-adrenalectomy values. There are no significant differences in the changes of SSPG titres between in pre-clinical Cushing's syndrome and in non-functioning adrenocortical adenoma. Systolic blood pressure, but not diastolic blood pressure, was also significantly decreased in the patients with adrenocortical adenoma. CONCLUSION High prevalences of disturbed glucose tolerance, insulin resistance and hypertension were found among the patients with non-functioning adrenocortical tumours. Adrenocortical adenoma may be one of the risk factors for insulin resistance that is believed to induce disturbed glucose tolerance and/or hypertension. Therefore, it is useful to evaluate insulin resistance for the patients with adrenal incidentalomas since results are likely to be helpful in deciding whether to remove the tumour by surgery.