A Rare Cause of Recurrent Hypoglycemia - The “Big-IGF-II” Factor

Abstract

Abstract Introduction: Hormone secreting tumors are a rare cause of hypoglycemia. Here we present an interesting case of paraneoplastic phenomenon resulting in a non-islet cell tumor causing hypoglycemia (NICTH) from a solitary fibrous tumor (SFT). Clinical Case: An 83-year-old female with a history of hypertension presented with recurrent episodes of lightheadedness and falls for one month. Review of systems was negative except for insignificant weight loss. Her vital signs and physical examination were unremarkable. Only significant finding on initial blood work was a blood glucose level of 30 mg/dL (n: >70mg/dL). Additional work-up of hypoglycemia revealed a low serum free insulin level 0.6 IU/mL (n:1.5 - 14.9 IU/mL), low proinsulin <4 pmol/L (n: <18.8 pmol/L), low C-peptide level 0.14 ng/mL (n: 0.80-3.85 ng/mL), low serum insulin-like growth factor-I (IGF-I) 33 ng/ml (n:34-246 ng/ml) and elevated IGF-II levels 370 ng/mL (n:47-350 ng/mL). Blood sulfonylurea and insulin antibodies screen were negative, ACTH and morning cortisol levels were within normal limits. A CT scan of chest, abdomen and pelvis for neoplastic workup demonstrated a large heterogeneous mass within the lower lobe of the right lung. A CT-guided biopsy disclosed spindle cell neoplasm, positive for signal transducer and activator of transcription-6 (STAT6) and CD34. Reverse transcription-polymerase chain reaction (RT-PCR) confirmed the NGFI-A binding protein 2 (NAB2) and STAT6 fusion which is specific for solitary fibrous tumor (SFT). She underwent surgical resection of the thoracic mass which resulted in complete resolution of her symptoms. Clinical Lessons: NICTH is a paraneoplastic syndrome associated with various benign and malignant tumors including SFT, hemangiopericytoma and metastatic hepatocellular carcinoma to name a few. Our case is an example of NICTH associated with SFT called Doege-Potter syndrome. The prevalence of hypoglycemia is seen in less than 5% of patients with SFT. It is often secondary to ectopic overexpression of unprocessed precursor ‘big’ IGF-II molecule, which binds to IGF-I receptor, resulting in tumorigenesis. An IGF-II/IGF-1 ratio is a sensitive marker and a value of more than 10 suggests excess production of IGF-II and is likely the cause of NICTH. Physicians should be cognizant of NICTH, especially in non-diabetic, otherwise healthy individuals in whom preliminary workup for hypoglycemia is negative and should look to identify any potential tumor as the likely cause. Surgical treatment is often the only curative option. Frequent meals, dextrose infusion, glucagon and growth hormone are bridging modalities until definitive surgical treatment.