Endocrine Abstracts

Introduction: Insulin autoimmune syndrome was first described in 1973 by Hirata, characterised by recurrent spontaneous postprandial hypoglycaemia. Serum insulin is extremely high with elevated insulin autoantibodies. More than 170 cases reported worldwide. We report the first case of IAS in Australia.

Case report: Eighty one-year old Argentinean woman with 3 month history of intermittent, late postprandial diaphoresis, tremors, palpitations, dizziness and confusion. Symptoms improved with sugary drinks and other caloric intake resulting in weight gain of 3 kg. At presentation blood glucose level (BGL) was 1.2 mmol/l and required 50% dextrose to maintain her BGL >6. Serum insulin was >2400 mU/l (normal <27), C-peptide 11.7 nmol/l (0.4–1.5) and sulphonylurea screening was negative. Abdominal CT, MRI and Dotatate PET scan failed to identify an insulinoma. Endoscopic ultrasound found an 8 mm pancreatic lesion. Calcium stimulation study showed high insulin without a gradient. Laparotomy failed to show an insulinoma. Diagnosis of Hirata disease with elevated insulin autoantibodies >50 U/l (<0.3) was treated with reducing prednisone dosage maintaining remission.

Discussion: Mechanism of IAS is that antibodies against insulin binds and releases insulin asynchronously. Free insulin levels are normal though bound (total) are high. Incidence of IAS in Caucasians is one-tenth of Japanese. Eighty percent of IAS patients spontaneously remit. In some individuals it is associated with exposure to sulfhydryl compounds interacting with disulphide bonds rendering insulin more immunogenic. IAS is strongly associated with HLA class II alleles. Insulinomas are the most prevalent cause of hyperinsulinemic hypoglycaemia in Caucasians. Investigation is focused on localization followed by surgery. Our case highlights important differential diagnosis, the need to measure insulin antibodies to avoid unnecessary surgery.