Introduction: Insulin autoimmune syndrome or Hirata disease is a rare cause of hypoglycemia without prior insulin exposure. Approximately 400 cases were reported, mostly in Japan. Its associated with other autoimmune diseases or exposure to sulfhydryl-containing drugs.
Case report: A 56-year-old Caucasian woman presented with a 20-month history of hypoglycemia ameliorated by sugar intake. She had a past history of autoimmune thyroiditis, asthma and factor XI deficiency. She wasnt taking any medication when evaluated, but had previously taken agomelatine, fluticasone/salmeterol, naproxen, acetylsalicylic acid and lorazepam. 72 h fast was negative. Prolonged 75 g oral glucose tolerance test (OGTT) revealed hypoglycemia after 240 min (39 mg/dl). Peak insulin was 5170 pmol/l (PerkinElmer AutoDELFIA®) at OGTT 120 min, with a recovery of 23% (>70%) after polyethylene glycol precipitation. Anti-insulin antibodies were strongly elevated at 600 U/ml (RiaRSR® IAA, reference <0.4). Gel filtration chromatography demonstrated high-molecular-weight insulin immunoreactivity suggesting the presence of insulin-antibody complexes. HLA typing revealed DRB1*04:04, DRB1*13, DQB1*04:02/DQB*06:03, DQA1*01:03/DQA1*03:01, the first and latter haplotypes being associated with Hirata disease. Patients clinical status improved after 1 g of methylprednisolone i.v. pulses for 2 days every 4 weeks. Two OGTTs during treatment revealed shorter insulin peaks with faster clearance than pre-treatment, however high titres of insulin autoantibodies were still measured. If clinical improvement resulted from the therapeutic approach or from spontaneous remission, which occurs in up to 80% of the cases, is unclear. Progressively lower insulin peaks during OGTT paralleled with persistently high insulin autoantibody titres may indicate that not all antibodies form insulin-antibody complexes in plasma. This leads to another challenge: how to best monitor disease activity during treatment?
Conclusion: Hirata disease should be considered in any patient with hyperinsulinemic hypoglycemia and positive anti-insulin antibodies. The presence of insulin-antibody complexes can influence the approach to the patient and should be tested. The best follow-up strategy is unknown.