A Case of Autoimmune Hypoglycemia (Insulin Autoimmune Syndrome)

Introduction: Insulin Autoimmune Syndrome (IAS) is a condition caused by Insulin Autoantibody (IAA). IAS was initially reported in 1970 by Yukimasa Hirata from Japan. From 1970 to 2009, 380 cases were reported worldwide. We report a case of IAS in an African-American man who had recurrent episodes of syncope secondary to hypoglycemia. Case Report: A 50-year-old African American man with hypertension presented to emergency room after syncope. His initial blood glucose (BG) was 27 mg/dl. After Dextrose and glucagon injection, BG became 270 and he regained consciousness without any deficit. Vital signs and physical examination were unremarkable. He was not on any medication, and had no access to insulin or oral hypoglycemic agents. No family history of endocrine disorders, malignancy or autoimmune diseases were reported. He had been hospitalized two times for syncope secondary to hypoglycemia. During hospitalization, fasting insulin level was >1000 IU/ml with high C-peptide (3.5ng/ml). Hypoglycemic agents assay was negative. During outpatient follow-ups, fasting labs showed C-peptide 1.59 ng/ml, Insulin antibody 37.6 U/ml while venous BG was 65 mg/dl. Random BG at different occasions were 65, 68 and 55 mg/dl. HbA1C was normal. BMI was gradually increased from 32.4 to 34.8 in 6 months. During the third hospitalization, fasting venous BG were 45 and 57 on two different days, Insulin was 2111 IU/ml and C-Peptide was 1.78 ng/ml. Other labs including cortisol and TSH were normal. CT abdomen was unremarkable. Discussion: In IAS, Insulin secreted after meal is bound by IAA. It causes hyperglycemia unchecked which triggers further insulin secretion. When the bound insulin dissociates from antibodies, it causes significant hyperinsulinemia and subsequent hypoglycemia. IAS can occur regardless of previous insulin exposure, as a solitary autoimmune manifestation or in association with other autoimmune disorders. It can be induced by drugs that contain sulfhydryl group. Etiology of IAS is still not fully understood but there are theories that genetic predisposition such as class II Human Leukocyte Antigen (HLA) and environmental triggers such as medications, viruses, hematological diseases etc. might play a role. In our patient, failure to test IAA in past admissions and lack of continuity of care delayed the diagnosis. Conclusion: IAS should be considered especially in those who have no clear etiology of hypoglycemia in order to avoid unnecessary diagnostic and therapeutic procedures. Gold standard test for definitive diagnosis is IAA. As IAS is frequently self-remitting, supportive management is usually recommended. In severe cases, pharmacotherapies that reduce insulin secretion and immunosuppressants are occasionally necessary. But there is still no study that compares different treatment measures.