SAT-485 Recurrent Pheochromocytoma and Mediastinal Mass in a Patient with SDHD-Associated Hereditary Paraganglioma-Pheochromocytoma Syndrome

Abstract Disclosure: S.I. Alqaisi: None. E. Lopez Hidalgo: None. A. Chunduru: None. P.R. Orlander: None. Background: Succinate dehydrogenase mutations are particularly associated with rare hereditary autosomal dominant conditions linked to a higher risk of malignant tumors and multifocal paragangliomas. Here we present a case of a patient with recurrent pheochromocytoma associated with SDHD mutation. Clinical Case: A 43-year-old man with a history of bilateral pheochromocytoma at the age of 8, status post-resection, and prior glioma of the carotid artery and vocal cord treated with chemotherapy and radiation, presented to the hospital with episodes of vomiting, abdominal discomfort, and diarrhea. Previous genetic testing had confirmed SDHD-associated hereditary paraganglioma and pheochromocytoma syndrome given family history of similar diagnosis. An abdominopelvic CT scan revealed a left adrenal gland measuring 4.7 cm transversely by 2.96 cm anteroposterior, with a 4.3 cm mass in the longitudinal dimension. Laboratory testing showed elevated serum normetanephrine (1327 pg/mL, normal <148 pg/mL), low serum-free metanephrines (<25 pg/mL, normal <57 pg/mL), and elevated total metanephrines (1327 pg/mL, normal <205 pg/mL). Urine catecholamine testing revealed elevated norepinephrine (498 mcg/24 hours, normal 15-100 mcg/24 hours) and dopamine (1940 mcg/24 hours, normal 52-480 mcg/24 hours) but normal epinephrine levels (<7 mcg/24 hours, normal 2-24 mcg/24 hours). An iodine meta-iodobenzylguanidine (MIBG) scan demonstrated increased tracer uptake in the 4 cm left adrenal mass, consistent with a neuroendocrine tumor, and a 7 × 6 × 5 cm mediastinal mass with radiotracer uptake suggestive of metastasis or another etiology. The patient developed hypertension, for which doxazosin was initiated. He also experienced tachycardia, requiring metoprolol administration before the procedure. The patient underwent laparoscopic left adrenalectomy, and histological examination confirmed a 4.4 cm pheochromocytoma. Cardiothoracic surgery and radiation oncology teams were consulted for the mediastinal mass; however, no immediate treatment was indicated. Outpatient follow-up was planned for further evaluation and management of the mediastinal mass. Conclusion: Recurrent pheochromocytomas are uncommon; however, they are most frequently observed in the context of SDHD mutations, which confer an increased predisposition to the development of paragangliomas and other neuroendocrine tumors, as demonstrated in this patient. These findings underscore the importance of genetic testing and close surveillance in patients with a history of pheochromocytoma, particularly those with a family history of similar diagnoses, to enable early detection and management of recurrence or associated tumors. Presentation: Saturday, July 12, 2025