Endocrine Abstracts

Introduction: Insulin autoimmune syndrome (Hirata’s disease) is a rare cause of hypoglycemia in Caucasians, with an estimated prevalence of 0,017 cases per 100.000 in general population. It is characterized by mostly postprandial hypoglycemia and the presence of autoantibodies against insulin. Treatment options include dietary modifications, glucocorticoids, azathioprine, rituximab and plasmapheresis.

Case report: A 72-year-old woman with no medical history of Diabetes Mellitus (HbA1c 5,6%) presented to our outpatient department reporting episodes of hypoglycemia (glu 40-60 mg/dl) since 2 months, the majority of which postprandially, accompanied by early post-meal hyperglycemia (glu 250-300 mg/dl). She presented an OGTT with glucose values compatible with DM (glu 0’: 104, glu 60’: 311, glu 120’: 256 mg/dl), concurrently with extremely high insulin values (ins 0’: 181, ins 60’: 1474, ins 120’: 5340 mIU/l). Such a combination raised the suspicion that insulin could not act properly. Prolonged OGTT was performed and hypoglycemia was recorded at 220’ (glu 33), while both insulin and C-peptide levels where profoundly increased (ins 220’: 169 μIU/ml, C-pept 220’: 11,3 ng/ml) simultaneously. After excluding some common causes of hypoglycemia (adrenal insufficiency, medications, alcohol abuse, malignancy), we proceeded with measurement of her insulin autoantibodies (anti-IAA), which turned out positive (>20 IU/ml – normal values <2,4). Our diagnosis was Hirata’s disease. Our patient’s medical history was free of exposure to susceptible drugs or recent infection. Treatment with methylprednisolone 15 mg daily was started and within a month her hypoglycemic episodes were significantly reduced. Two months later her antibody titre was within normal range (2 IU/ml), and remained within normal limits (1 IU/ml) at follow-up measurement 4 months later, even after treatment discontinuation. She reports no hypoglycemic episodes.

Conclusion: Despite the rarity of this condition, Hirata’s disease is important to be considered early in the differential diagnosis of hypoglycemia. This case report aims to raise awareness of this clinical condition to the physicians, since a high titre of insulin autoantibodies would help avoid costly and complicated examinations.