An adrenal mass and increased catecholamines: monoamine oxidase or pheochromocytoma effect?

Hormonal evaluation in patients with an adrenal incidentaloma can be difficult in patients with comorbidities or in patients using interfering drugs. We present a case of a 54-year-old man who was evaluated for an adrenal mass. The medical history reported treatment with a monoamine oxidase (MAO) inhibitor for recurrent psychoses. Hormonal screening showed elevated levels of normetanephrine and metanephrine in plasma and urine, suggesting a diagnosis of pheochromocytoma (PHEO), and an adrenalectomy was performed. Histologic examination showed that the tumor had an origin of the adrenal cortex. MAO inhibitors are also known to cause elevated levels of catecholamines. In this case, a PHEO seemed more likely the cause due to repeatedly elevated levels of metanephrines and normal levels of catecholamines. Since the tumor had an origin of the adrenal cortex, the use of MAO inhibitors was the most likely explanation for the elevated levels of metanephrines. This case illustrated the difficulties in diagnosing PHEO, especially in patients with comorbidities and interfering drugs.