Metastatic Insulinoma Presenting After Bariatric Surgery in a Patient Subsequently Diagnosed With MEN 1

Abstract

Background: Hypoglycemia is a recognized complication of bariatric procedures due to changes in the gut hormonal milieu. Possible causes of hypoglycemia include dumping syndrome, nesidioblastosis and rarely insulinoma. MEN1 is a heritable disorder characterized by the occurrence of parathyroid, anterior pituitary and pancreatic islet cell tumors. Clinical Case: A 48 yo female with HTN, depression, PCOS, primary hyperparathyroidism s/p 3.5 gland parathyroidectomy 2008, facial angiofibroma 2011, obesity s/p gastric sleeve 2018, and a history of DMT2 presented with frequent episodes of hypoglycemia. DMT2 was diagnosed in 2003, but all DM drugs were withdrawn shortly after sleeve gastrectomy. One year after surgery, she started to develop primarily fasting hypoglycemia in the 40-50 mg/dl range confirmed on CGM. Symptoms included perioral numbness, diaphoresis and confusion which resolved with glucose tablets. She reported a 7 kg weight regain due to eating every 2 hours to minimize episodes but symptoms progressed. Family history was significant for HTN and DM. A 72 hour fast confirmed hyperinsulinemia with symptomatic hypoglycemia at a serum glucose of 37 mg/dl, a suppressed ß-hydroxybutyrate of 0.6 mmol/L, elevated proinsulin 7.7 ρmol/L and inappropriate normal c-peptide 0.8 ng/mL. The oral hypoglycemic panel was negative. A pancreatic protocol CT revealed a 1.2 cm heterogeneous arterial enhancing lesion in the body of pancreas, a 0.6 cm focus in the tail of pancreas, a 1.6 cm enhancing lesion in the liver and a 1.4 cm abdominal wall mass. Genetic testing was positive for MEN-1 and additional biochemical evaluation including VIP, gastrin and glucagon was negative. A pituitary MRI was unremarkable. She underwent an ex-lap, partial hepatectomy, distal pancreatectomy, splenectomy, and resection of the duodenal mass. The pancreas had multiple NETs, largest was 1.6 cm and stained positive for insulin. The liver mass demonstrated a metastatic well differentiated NET. The 1.7 cm duodenal mass was consistent with a leiomyoma. All surgical margins were negative, but focal lymphovascular and perineural invasion was identified with negative lymph nodes (0/27). She was diagnosed with a metastatic insulinoma with histopathology revealing a well differentiated neuroendocrine tumor G1, <1mitosis/2mm2, Ki-67 less than 3%, stage pT1N0M1. Hypoglycemia resolved post-operatively. Conclusion: Hypoglycemia predominantly in the fasting state, worsening shortly after bariatric surgery, or refractory to dietary or medical management should be further evaluated to exclude insulinoma. Given her medical history, there was concern for MEN-1, thus prompting genetic testing. Unlike with sporadic cases, there is a higher rate of recurrence with MEN-1 associated insulinoma. Highly unusual is also the finding of metastatic disease, occurring only in 4- 14% of all insulinoma cases.