Think Outside the Thorax: Doege-Potter Syndrome Presenting as a Retroperitoneal Mass

Introduction: Non-islet cell tumor hypoglycemia (NICTH) is a rare paraneoplastic syndrome, occurring less commonly than insulinoma. These tumors produce high molecular weight insulin-like growth factor-2 or “big IGF-2”, resulting in hypoglycemia: big IGF-2 decreases glycogenolysis, gluconeogenesis, and glucagon release as well as increases glucose uptake by adipocytes and skeletal muscle. NICTH specifically associated with a solitary fibrous tumor (SFT) is known as Doege-Potter syndrome. Doege-Potter syndrome is seen most with thoracic SFT’s. This case study details the diagnosis and management of Doege-Potter syndrome due to retroperitoneal SFT. Case Description: Our patient is a 68-year-old, white female who initially presented to an outside facility with a 3-week history of episodic neuroglycopenic symptoms temporarily relieved with eating. She reported night sweats but no weight change or fever. Medical history was notable only for hypertension and GERD. She had no personal or family history of diabetes. She was transferred to our facility for further evaluation of an 18.6 cm multilobular mass seen just inferior to the liver on abdominal CT. Whipple’s triad was confirmed with venous glucose sampling while inpatient. C-peptide, free/total insulin, and pro-insulin were collected during permissive hypoglycemia and were low. Morning cortisol and TSH were unremarkable. Additionally, sulfonylurea screen and insulin antibodies were negative. Ultrasound-guided biopsy of the lesion was positive for CD34 and STAT6, consistent with SFT. Refractory hypoglycemia was treated with D5W infusion until surgical resection of the retroperitoneal mass, after which, she had complete resolution of her hypoglycemia. Discussion: This patient’s serum IGF-2 was within normal limits, consistent with reports of feedback inhibition exerted by increased levels of big-IGF-2. Therefore, the IGF-2:IGF-1 ratio is used to determine increased serum levels of big IGF-2, but this test is not widely available. SFT’s can recur within months to years of resection, necessitating surveillance. Recurrence is also more common with extrathoracic tumors. Surgical pathology noted tumor dimensions of 22 cm and 2270 g; mitotic rate was 1 per 10 hpf. Features typical of malignancy include large size (>15 cm) and mitotic rate >4 mitoses per hpf. This patient’s follow-up CT abdomen at 6 weeks did not show any findings to suggest recurrent or metastatic disease.