THU392 Type B Insulin Resistance: A Rare Cause Of Hypoglycemia

Disclosure: S.Z. Bhat: None. A. Sidhaye: None. A.H. Hamrahian: None. Introduction: Non-diabetic hypoglycemia in patients with diabetes mellitus is rare. Type B insulin resistance syndrome (TBIRS), caused by insulin receptor antibodies, presents with severe insulin resistance, but can uncommonly result in a hypoglycemic picture. Clinical Case: A 59-year-old woman with a history of SLE, T2DM, and primary hyperparathyroidism was admitted for acute confusion and found to have a POC glucose of 30 mg/dl. Her symptoms improved after IV glucose administration. She was on a stable basal-bolus insulin regimen of 0.8 U/kg/day and had unintentional 100-pound weight loss over 1 year. Significant exam findings included BMI of 29 kg/m(2), gingival hyperplasia, and acanthosis nigricans. Aside from insulin, she took no medications strongly associated with hypoglycemia. Labs including CBC, CMP, TFTs, and morning cortisol were normal. HbA1C and adiponectin levels were 7.7%, and 28 µg/ml (5-28), respectively. Given the suspicion of exogenous insulin-mediated hypoglycemia, only correctional insulin was used during hospitalization. She had a repeat hypoglycemic episode on the 2(nd) day with minimal insulin use. A 72-hour fasting test showed a whole blood glucose of 44 mg/dL with concurrent serum C-peptide of 1.72 ng/mL, serum insulin 55 mIU/L and pro-insulin 21.9 pmol/L 12 hours into fasting. MRCP showed an 11 mm cystic lesion in the pancreas and widespread lymphadenopathy. The CGM noted significant fasting and post-prandial hypoglycemia. Diagnosis of insulinoma was considered unlikely due to persistent post-prandial hyperglycemia. Oral hypoglycemic panel and insulin autoantibodies were negative. The patient’s history of SLE, high-normal adiponectin, history of hyperglycemia and the presence of acanthosis nigricans favored work-up for insulin resistance syndromes. Due to the non-availability of insulin receptor antibody testing in the US, blood work was sent to Dr. Lutz Schomburg’s lab at Institute for Experimental Endocrinology, Berlin, Germany. The patient’serum was positive for insulin receptor antibodies, tested via an immunoassay technique, with elevated binding index (BI) of 248, 251 and 247 on 3 different samples of the patient, and normal binding index in the control sample, leading to the diagnosis of type B insulin resistance syndrome (BI >3 is positive, >10 indicates high positivity). The patient was treated with diet modification and CGM use, with improvement in the frequency of hypoglycemic episodes. She declined immunomodulation therapy. Conclusion: Hypoglycemia is an uncommon presentation of TBIRS and should be considered in the differential of non-diabetic hypoglycemia, particularly in patients with a history of auto-immune disease. The mechanism for hypoglycemia is purported to be an insulin-mimetic effect of insulin receptor antibodies at low titers. Presentation: Thursday, June 15, 2023