SAT-501 - Obstructive Sleep Apnea Mimicking Pheochromocytoma: A Reversible Cause of Catecholamine Excess

Introduction:
Pheochromocytoma is a catecholamine-secreting tumor associated with paroxysmal hypertension and adrenergic symptoms. Similar clinical and biochemical findings may occur without an identifiable tumor, termed pseudopheochromocytoma. Obstructive sleep apnea (OSA) is an underrecognized cause of sympathetic activation that can lead to transient catecholamine elevation and mimic pheochromocytoma. We present a case of severe OSA with biochemical findings mimicking pheochromocytoma.

Case description:
An 85-year-old woman with severe obstructive sleep apnea (OSA) and a 9-year history of refractory hypertension was referred for evaluation of secondary causes. Her blood pressure remained poorly controlled despite four antihypertensive agents, with home readings ranging from 150–170 mmHg and intermittent episodes exceeding 200 mmHg systolic. She reported increased sweating and occasional upper body flushing but denied headaches, palpitations, or anxiety.
Initial biochemical evaluation revealed markedly elevated 24-hour urinary normetanephrine (1,839 µg/24 h; reference < 612) and metanephrine (483 µg/24 h; reference < 209), while vanillylmandelic acid levels were within normal limits. Abdominal MRI showed no adrenal or extra-adrenal mass. The patient had previously been diagnosed with severe OSA (apnea–hypopnea index 36.8 events/hour) but was poorly adherent to continuous positive airway pressure (CPAP) therapy.
Following re-initiation of CPAP with improved adherence, repeat testing one month later with plasma free metanephrines demonstrated normalization of values. Her blood pressure also improved without changes to her antihypertensive regimen.

Discussion:
This case demonstrates pseudopheochromocytoma, a clinical syndrome characterized by paroxysmal hypertension and symptoms suggestive of catecholamine excess in the absence of an identifiable catecholamine-secreting tumor. Biochemical findings may show normal or modest elevations in catecholamine metabolites, which can complicate the diagnostic evaluation and mimic pheochromocytoma.
Several reports have described an association between obstructive sleep apnea (OSA) and pseudopheochromocytoma-like presentations. The proposed mechanism involves recurrent hypoxia and sleep fragmentation leading to sustained sympathetic activation and intermittent elevations in circulating catecholamines. Prior studies have shown that a significant proportion of patients with OSA and hypertension may have elevated urinary normetanephrine levels.
This case is notable for demonstrating normalization of metanephrine levels following adherence to CPAP therapy, supporting a reversible mechanism linking untreated OSA to false-positive biochemical findings. Recognition of this relationship is important to avoid unnecessary diagnostic workup and misdiagnosis.

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