THU615 Rhabdomyolysis: A Rare Presentation Of Extra-adrenal Neuroendocrine Tumor

Disclosure: M. Saleem: None. S.M. Harman: None. J. Targovnik: None. Introduction:Paraganglioma is a rare neuroendocrine tumor (NET) arising from neural crest progenitors located outside of the adrenal gland and predominantly produce norepinephrine if functional. Here, we present a case of epinephrine producing extra-adrenal sympathetic neuroendocrine tumor. Case: A 66-year-old male with history of resistant hypertension (on amlodipine, lisinopril & metoprolol), hyperlipidemia & obesity presented for evaluation of possible pheochromocytoma/paraganglioma. He reported paroxysmal episodes of muscle spasm & paresthesia accompanied by hypertension (up to 200 mm Hg), palpitation, sweating & tremor lasting about 30-60 minutes. His CPK was elevated up to 428 U/L (NR 30-170 U/L) during those episodes. He reported 7 "major episodes" beginning ∼15 years prior to diagnosis, of which 3 occurred after major surgery with "small episodes" occurring monthly, exacerbated by sun & heat. Family history was remarkable for sister with recurrent rhabdomyolysis. Labs showed elevated epinephrine 181 pg/ml (normal <57), Dopamin 67 pg/ml (normal <10) and normal norepinephrine, significantly elevated 24h urine metanephrine 855 mcg/24h (normal 90-315), normal normetanephrine & dopamine levels. CT showed a 2.2 x 2.2 x 2.1 cm retroperitoneal mass with 84% absolute concerning for possible paraganglioma. FDG-PET and DOTATATE showed hypermetabolic activity (SUV max 6.63) and DOTATATE avid left retroperitoneal mass respectively. After discontinuing beta blocker and optimizing alpha blockage with doxazosin, the patient was referred to endocrine surgery and had a successful resection of this mass and left adrenalectomy. Pathology was consistent with chromaffin cell neoplasm and normal left adrenal gland. Patient had clinical and biochemical resolution of his symptoms post-op. Genetic counseling was done with pending results. Discussion: Pheochromocytomas & paragangliomas (PPGLs) are rare NET arising from chromaffin cells of the adrenal medulla or neural crest progenitors located outside of the adrenal gland, and predominantly produce epinephrine and norepinephrine respectively. Adrenal medullary tissue secretes epinephrine due to the activity of PNMT, induced by high local levels of cortisol from the adrenal cortex, which attaches a methyl radical to the catechol amino group. Extramedullary sympathetic secretory cells normally lack this enzyme and secrete norepinephrine. Thus, it is likely that the neoplasm we report had ectopic expression of this enzyme. PPGLs have variable signs and symptoms which mainly reflect the hemodynamic and metabolic actions of the catecholamines produced and secreted by the tumors with hypertension being the most common sign. Rhabdomyolysis is an unusual manifestation. This case is unique in that it presented as an extra-adrenal NET predominantly produced epinephrine and presented with rhabdomyolysis. Presentation: Thursday, June 15, 2023