MON-386 Finding Truth from Two False-Positives

Abstract

Certain medications can interfere with catecholamines levels and result in a misleading diagnosis of pheochromocytoma. Tricyclic antidepressants, alpha-blockers, beta-blockers, and acetaminophens are the most common cause of falsely elevated levels of catecholamines. To confirm and localize pheochromocytoma, 123I-Metaiodobenzylguanidine (123I-MIBG) scintigraphy scan is usually performed following a biochemical test if CT or MRI has failed to detect the tumor. Here we describe a 48-year-old African-American male who was found to have a medication-related elevation in catecholamines with positive 123I-MIBG adrenal uptake. He was referred to the endocrinology clinic for elevated plasma epinephrine, norepinephrine, and dopamine levels. His primary care physician obtained catecholamines levels for recurrent episodes of anxiety, sweating, and dizziness. No history of hypertension was noted. His medications include alprazolam for anxiety, hydrocodone/acetaminophen for chronic back pain, valproic acid for mood-stablilizing, and escitalopram for depression. At the first visit, his blood pressure was 162/110. Otherwise, an unremarkable physical exam was noted. Initial blood work at an outside facility showed plasma dopamine > 3000 pg/mL (Ref 0-20 pg/mL), epinephrine 6827 pg/mL (Ref 0-62 pg/mL), and norepinephrine 51919 pg/mL (Ref 80-520 pg/mL). The patient underwent MRI of the abdomen and pelvis before the referral, which was unremarkable, and had an 123I-MIBG scan that showed increased accumulation over the left adrenal gland; none was seen over the right adrenal gland. We withheld his medications except for alprazolam. Catecholamine levels were retested after four weeks and showed normal plasma epinephrine, norepinephrine, metanephrine, and normetanephrine levels. The 123I-MIBG scan is highly sensitive and specific for the detection of pheochromocytoma. However, 123I-MIBG uptake can also be seen in normal adrenal medulla (16% of scans after 48 h). The pattern of 123I-MIBG uptake may be asymmetrical between the left and right adrenals, and therefore, caution should be applied in interpreting the images obtained, particularly to avoid unnecessary or misguided surgery. This case demonstrates a unilateral 123I-MIBG adrenal uptake possibly associated with medications. It is expected that the uptake would be bilateral, given the systemic effect of the medications. Nonetheless, in this case, unilateral adrenal uptake was found. Medication-induced catecholamine elevation has to be ruled out before further investigation for pheochromocytoma. This step is crucial given the non-specific symptoms of pheochromocytoma and the possibility of having false catecholamines elevation and false 123I-MIBG uptake, both of which further challenge the diagnosis of pheochromocytoma.