Endocrine Abstracts

Insulin autoimmune syndrome (IAS), or Hirata disease, is a rare cause of hypoglycemia mediated by insulin autoantibodies (IAA). We report a 76-year-old Caucasian male with hypertension, ischemic heart disease, and benign prostatic hyperplasia who presented with recurrent syncope and seizure-like activity over two months, necessitating his third hospital admission. Initial workup, including CT/MRI brain, EEG, echocardiogram, and Holter monitoring, was unremarkable. During the third admission, hypoglycemia was confirmed (serum glucose 2.2 mmol/l), with markedly elevated insulin (>6945 pmol/l), C-peptide (2.48 nmol/l), and IAA titers (75%, normal <5.5%). Pancreatic imaging and endoscopic ultrasound excluded neuroendocrine tumours, and negative sulfonylurea screen confirmed IAS. The patient received intravenous hydrocortisone for two days, followed by oral prednisolone, dietary counselling for frequent low-carbohydrate meals, and continuous glucose monitoring. Rituximab was initially considered for severe, refractory hypoglycemia but was not administered due to rapid clinical and serological improvement. Follow-up revealed declining IAA titers and no further hypoglycemic episodes by five months. Historically prevalent in Japan (0.017/100,000), IAS is associated with HLA-DR4 (DRB1*0406) and triggers including sulphydryl drugs or viral infections. Rising global cases among Caucasians likely reflect increased medication use and wider IAA assay availability. IAS involves high-capacity, low-affinity IAA causing glycemic fluctuations through insulin-IAA complex dynamics. Symptoms range from mild to severe (seizures, syncope). Management is complex given an 82% spontaneous remission rate. This case highlights recognising IAS in non-Asian populations and demonstrates the efficacy of corticosteroids and dietary interventions. Recurrence is rare (<5%).