Paraneoplastic Hypoglycemia Leading to Insulin Independence in a Patient With Type 1 Diabetes

Introduction: Hypoglycemia is a rare paraneoplastic manifestation of several non-islet cell tumors (NICT) that is rarely reported in individuals with diabetes. We report the first case of a patient with type 1 diabetes (T1D) and a recurrent gastrointestinal stromal tumor (GIST) who required discontinuation of all insulin therapy with continuous parenteral glucose infusions to avoid hypoglycemia. Case: The patient is an underweight (BMI 14.9 kg/m(2)) 59-year-old female with a 24-year history of T1D treated with insulin pump therapy who was diagnosed with GIST in 2003. Following surgical resection with postoperative adjuvant therapy, she remained tumor free until 2012 when she had disease recurrence unresponsive to several tyrosine kinase inhibitors. In 2014, she reported frequent episodes of documented hypoglycemia despite continued reductions in basal insulin infusion rates. Laboratory testing following several hours of insulin discontinuation revealed undetectable insulin and C-peptide levels, low IGF-1, normal IGF-2, and an IGF-2: IGF-1 ratio of 7.86. Thyroid, kidney and adrenal tests were normal. Initiation of prednisone alone then in combination with octreotide did not abate the hypoglycemia. During a hospitalization for hypoglycemia, exogenous insulin therapy was discontinued and 10% dextrose infusions started. Attempts at weaning the dextrose infusions resulted in hypoglycemia, prompting insertion of a PICC line prior to discharge home with continuous 25% dextrose infusions at 40-60 mg per hour. Discussion: NICT hypoglycemia (NICTH) is characterized by excessive tumor production of IGF-2 or pro-IGF-2. The structure of IGF-2 is similar to insulin, allowing cross reactivity at the insulin receptor. IGF binding proteins (IGFBPs) are responsible for transporting IGF-2 in plasma. Abnormal processing of the gene for IGF-2 results in increased production of the more biologically active pro-IGF-2 that does not form a complex with IGFBP3 and is available to interact with insulin receptors. In patients with normal IGF-2 (chronic kidney disease, poor nutritional status), an IGF-2: IGF-1 ratio >3 can be used to confirm NICTH. IGFBP-3 was not measured in this patient but it is likely this was low due to her poor nutritional status. The most definitive treatment for NICTH is resection of the tumor. Pharmacological management can be considered in patients who are not surgical candidates, but is not always successful as was observed in this patient. Conclusion:This is an unusual case of malignancy associated hypoglycemia in a woman with type 1 diabetes who required discontinuation of all insulin therapy as well as continuous dextrose infusions to achieve euglycemia and briefly maintain an acceptable quality of life over a period of several months.