MON-540 - Using Clonidine Suppression Testing to Distinguish Essential Hypertension and Pheochromocytoma

Background: Pheochromocytomas are rare and can be difficult to distinguish from essential hypertension

Clinical

Case: A 75-year-old male presented with an adrenal incidentaloma found on imaging for planning an abdominal aortic aneurysm (AAA) repair. He has had hypertension onset in the past 4-5 years. He has episodes of chest pain and anxiety during which he becomes clammy. His wife reports he turns white during these episodes. He never had issues with anxiety in the past but now is on medication to manage this. There is no family history of endocrine disorders. Review of his imaging showed in in 2017 he had some mild nodularity of the left adrenal gland that grew to a 2.4 cm nodule by 2023. His labs were not concerning for cortisol excess but were concerning for possible pheochromocytoma; plasma norepinephrine 1824 pg/mL (n 0-874), normetanephrine 319 pg/mL (n 0-285) and urine normetanephrine 1138 pg/mL (n 58-276). Due to concern for adrenaline excess his AAA repair was placed on hold. The patient wanted to avoid adrenal surgery unless it was necessary. Though the patient’s catecholamine levels were elevated above the normal range they were in the range of overlap with essential hypertension, thus clonidine suppression confirmatory testing was pursued. The patient’s catecholamine levels did not suppress (~ 20% drop) in response to 0.3 mg of clonidine thus confirming pheochromocytoma. Endocrinology, anesthesiology and surgery worked closely on this case to optimize the patient’s blood pressure before surgery. Blood pressure was managed with prazosin, amlodipine and metoprolol. He had no significant intraoperative instability but had post operative hypotension and down titration of blood pressure medications. At 6 month follow up his normetanephrine levels were normalized and he was able to undergo AAA repair. Genetic testing did not reveal any hereditary syndromes.


Conclusion: Using clonidine suppression testing confirmed diagnosis of pheochromocytoma in this patient with mildly elevated catecholamines.

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