MON-332 - The GIST of Hypoglycemia: A Rare Case of Non-Islet Cell Tumor Hypoglycemia Secondary to GI Stromal Tumor

Introduction:
Non–islet cell tumor hypoglycemia (NICTH) is a rare cause of fasting hypoglycemia. Unlike insulinomas, which are the most common cause of tumor-mediated hypoglycemia and mediate hypoglycemia by insulin release, non-islet cell tumors cause hypoglycemia by overproduction of insulin-like growth factor 2 (IGF2) and its precursor, “big” IGF2. IGF2 exerts insulin-like activity and causes hypoglycemia by binding to IGF and insulin receptors. Gastrointestinal stromal tumors (GIST) are an uncommon but documented cause of NICTH.

Case Description:
A 66-year-old male with history of GIST and known intraabdominal metastases presented with 4-days of confusion, emotional lability, and “child-like” behavior. He was found to be hypoglycemic with capillary glucose level of 27mg/dL. He had no history of diabetes. There was no clinical evidence of sepsis, liver failure, or alcohol use. Intravenous dextrose rapidly improved both his hypoglycemia and mentation. In the setting of known GIST, there was high suspicion for NICTH, and a 72-hour fast was conducted. At the time of documented hypoglycemia (serum glucose < 55mg/dL), insulin, pro-insulin, and c-peptide levels were appropriately suppressed. B-hydroxybutyrate and growth hormone were within normal limits. Sulfonylurea screen was negative. IGF1 level was low at 18ng/mL (normal 37-236) and IGF2 level was 100ng/mL (normal 180-580), with a IGF2/IGF1 ratio of 5.5. Cortisol level from the episode of hypoglycemia was 19.6mcg/dL, ruling out adrenal insufficiency. The patient was started on cornstarch 4 tablespoons (28g carbs) every 6 hours, allowing discontinuation of IV dextrose and maintenance of euglycemia. Oncology was consulted; they currently plan to enroll the patient in a clinical trial of Imatinib and Zoftomenib after discharge.

Conclusion:
We highlight GIST as a rare etiology of NICTH and demonstrate the diagnostic approach for NICTH, which should be conducted during an episode of hypoglycemia. IGF2/IGF1 ratio >10 confirms the diagnosis, while IGF2/IGF1 ratio between 3 and 10 may still be consistent with NICTH. IGF2 levels may or may not be elevated. This is because hypoglycemia may be mediated by increased “big” IGF2 levels as opposed to mature IGF2 levels, and if the IGF2/IGF1 ratio is < 10, direct measurement of “big” IGF2 should be performed. Definitive treatment is through treatment of the underlying tumor, through surgical resection, systemic therapy, or radiation. Treatment of hypoglycemia is supportive, with increased oral intake or IV dextrose. Glucocorticoids, somatostatin analogs, subcutaneous growth hormone, diazoxide, and even glucagon infusion pumps have been used as well. Uncooked cornstarch has also been shown to be effective due to its slow digestibility. Our case proved that uncooked cornstarch is indeed an effective therapy for glycemic stabilization while definitive oncologic management is pursued.

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