Frequency of pheochromocytoma in adrenal incidentalomas and utility of the glucagon test for the diagnosis.

To investigate the frequency of pheochromocytoma in patients with incidentally discovered adrenal masses (incidentalomas) and to evaluate the sensitivity, specificity and diagnostic accuracy of the Glucagon test in comparison with resting plasma catecholamines, 89 patients with adrenal incidentalomas (age range 23-80 yr; 41 males and 48 females) were studied. Fifty-seven patients were normotensive (SBP 130+/-1.8 mmHg; DBP 80+/-0.7 mmHg, mean+/-SE) and 32 had stable hypertension (SBP 155+/-3.3 mmHg, DBP 93+/-1.4 mmHg): no patient complained of typical signs or symptoms of pheochromocytoma. Resting plasma samples for noradrenaline and adrenaline determination and, at appropriate intervals, the Glucagon test (1 mg i.v.), were performed in all subjects. Diagnosis of pheochromocytoma was made on the basis of humoral evaluations and/or surgical intervention in 6 patients (6.7%), of whom 3 hypertensives and 3 normotensives. Resting plasma catecholamines revealed 5 out of 6 patients with pheochromocytoma: in 3 cases both catecholamines were above the normal range, in 1 only adrenaline was elevated and in 1 case only noradrenaline. Similarily, the glucagon test identified 5/6 pheochromocytomas: in 3 patients the response was abnormal for both catecholamines, in 1 only for adrenaline and in 1 case only for noradrenaline. The sensitivity, specificity, and diagnostic accuracy of resting plasma catecholamines and of the glucagon test were comparable: 83.3%, 96.3%, and 95.5%, respectively. In conclusion, the frequency of pheochromocytoma in adrenal incidentalomas is not negligible, and since the diagnostic accuracy of the Glucagon test is the same of that of resting plasma catecholamines, the former does not appear to offer additional advantages in the diagnosis of incidentally discovered pheochromocytomas.