MON-078 - A Palpitating Diagnosis: A Case of Rare Thoracic Paraganglioma

Background:
Paragangliomas (PGL) are extra-adrenal neuroendocrine tumors that arise from chromaffin cells. Oftentimes, the diagnosis of paraganglioma (PGL) can be elusive despite a high degree of suspicion. We present a rare case of thoracic PGL.

Clinical

Case:
A 27-year-old female with history of polycystic ovary syndrome and hypothyroidism presented with worsening anxiety and tachycardia. Thyroid hormone levels were normal, and further history revealed that she also had intermittent facial redness, diaphoresis, dizziness, and nausea. Labs showed a plasma metanephrine 0.19 (0-0.49 nmol/L) and normetanephrine 14.40 (0-0.89 nmol/L). 24-hour urine metanephrines were also elevated.

Abdominal MRI showed no abnormality, and full body MIBG SPECT/CT was also negative. Given her symptoms and biochemical findings, an extra-adrenal PGL was suspected. Further investigation utilizing 68Ga-DOTATATE PET/CT showed a Dotatate avid subcarinal mass. She had preoperative preparation with phenoxybenzamine and metoprolol and underwent thoracotomy on cardiopulmonary bypass with successful mass resection. Pathology confirmed PGL, 5.0 x 7.3 cm without invasion. Genetic testing revealed a variant of uncertain significance (VUS) in the succinate dehydrogenase subunit B (SDHB) gene, subsequently reclassified as pathogenic. There was no known family history. Seven years after resection, patient has been medically stable without recurrence of tumor.

Discussion:
We present a rare case of thoracic PGL associated with elevated catecholamine levels. Despite initial standard imaging, our patient’s subcarinal mass was not detected on initial evaluation. However, given a high index of suspicion, further imaging was warranted. Potential modalities for PGL assessment include 68Ga-DOTATATE PET/CT, 123I-MIBG, 18F-FDOPA, and 18F-FDG, of which 68Ga-DOTATATE scans have the highest diagnostic accuracy, and successfully localized the thoracic PGL in our patient.

Genetic testing is also recommended for all patients diagnosed with PGL. Our patient had a variant of uncertain significance (VUS) of the succinate dehydrogenase subunit B (SDHB) gene, one of three SDHx variants associated with PGL predisposition. Of note, immunohistochemical staining in this case showed loss of SDHB protein, supporting reclassification of the VUS found in this patient as pathogenic. SDHB gene variants are more frequently associated with thoracic PGLs and confer a higher risk of malignancy, with carriers requiring lifelong surveillance.

Initial medical management is with alpha-blockers followed by beta-blockers for both symptom management and preoperative preparation. Definitive management of PGLs remains surgical intervention. This case of rare thoracic PGL underscores the components of a thorough biochemical and genetic evaluation of PGL and the various imaging modalities available to locate an elusive tumor.

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