SUN-499 - Silent Pheochromocytoma Presenting as Refractory Hyperglycemia without Classic Adrenergic Symptoms

Background: Pheochromocytoma is a rare catecholamine-secreting tumor that typically presents with episodic headache, diaphoresis, and hypertension, but may rarely present without classic adrenergic symptoms. Catecholamine-induced dysglycemia is an underrecognized cause of refractory hyperglycemia.

Case Presentation: A 42-year-old non-obese man with a history of semi-controlled diabetes mellitus and hypertension presented with severe refractory hyperglycemia (HbA1c 14.7%) and mild hypercalcemia (10.8–11.1 mg/dL). Latent Autoimmune Diabetes of Adults (LADA) was ruled out. Despite intensive treatment with basal–bolus insulin and a hybrid closed-loop insulin pump, glycemic control remained highly variable. He denied headache, palpitations, diaphoresis, and paroxysmal hypertension. Routine abdominal ultrasound for evaluation of fatty liver and subsequently triphasic CT imaging showed a 6.1 cm left adrenal indeterminate mass. PET/CT demonstrated mild FDG uptake (SUVmax 3.8) without evidence of metastasis. Biochemical testing showed plasma metanephrine (731 pcg/ml) and normetanephrine (2023 pg/ml), with 24-hour urine epinephrine (402 mcg), norepinephrine (1027 mcg), normetanephrine (3682 mcg), VMA (14 mcg), and metanephrine (2932 mcg). Other adrenal hormonal work-up was within normal limits.

Management and Outcome: Laparoscopic left adrenalectomy after appropriate alpha and beta blockade was performed. Postoperatively, blood pressure and hyperglycemia normalized completely without needing insulin or antihypertensive therapy. Follow-up biochemistry showed normalization of catecholamine levels, and pathology demonstrated a benign pheochromocytoma.

Conclusion: This case highlights silent pheochromocytoma as a rare and reversible cause of refractory hyperglycemia. Severe insulin resistance initially attributed to poor adherence was secondary to catecholamine excess, underscoring the importance of early suspicion, as timely surgical resection can lead to resolution of hyperglycemia and prevent long-term metabolic complications.

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