A 53-year-old woman visited the emergency room of our hospital complaining of headache, palpitation, and chest discomfort. She was diagnosed with Graves' disease at a different hospital 1 month prior to being admitted at our hospital and had been taking both methimazole 40 mg/day and β-blocker since her diagnosis. Prior to visiting our emergency room, she consumed breakfast and was measured with a serum glucose level of 294 mg/dL. Laboratory studies including complete blood cell count with differential, chemistry profile, and electrolytes were all within normal limits. The result of thyroid function tests were TSH <0.01 µIU/mL, free T4 2.74 ng/dL, and T3 184.8 ng/dL. The patient's symptoms were initially attributed to hyperthyroidism due to the lack of abnormal findings on neurologic exam and brain magnetic resonance imaging. However, 6 hours after discharge, the patient revisited our emergency room due to sweating and altered mental state, where it was noted that she had neither a history of diabetes mellitus nor previous exposure to insulin or oral antidiabetic agents. Furthermore, there was no family history of thyroid disease and diabetes mellitus. The patient's initial serum glucose level was 27 mg/dL, HbA1c was 5.8%, serum total insulin was 600 µIU/mL, and serum C-peptide was 15.3 ng/mL. The titer of insulin autoantibody was 84.8%, while detection of both insulin receptor antibody and islet cell antibody were negative. The percent of 125I-insulin binding was not measured. The titers of serum thyroid autoantibodies were high. Specifically, antithyroid peroxidase antibody was 2,876 U/mL (normal range, 0 to 100), antithyroglobulin antibody was 330 IU/mL (normal range, 0 to 115), and TSH receptor antibody was 2.95 IU/L (normal range, <1.22). A CT scan revealed no evidence of insulinoma or extrapancreatic neoplasm. The patient's fasting insulin level was more than 3,000 µIU/mL and C-peptide was 25.9 ng/mL on hospital day 7. A 75-g oral glucose tolerance test showed marked increase of total insulin level and subsequent hypoglycemia developed after 240 minutes (). HLA genotyping was performed by sequence based typing and the result was HLA-DRB1*0406 and *1501. Continuous intravenous glucose injection was needed due to recurrent fasting hypoglycemia. Methimazole-induced insulin autoimmune syndrome was diagnosed, and methimazole was subsequently discontinued. Hypoglycemic episodes disappeared after 1 month, with the patient consuming small frequent meals and a low carbohydrate diet. The concentration of serum total insulin, titer of insulin autoantibody, and serum C-peptide level decreased gradually after 5 months (). Radioactive iodine therapy with 131I 15 mCi was performed to address Graves' disease in the patient.
This patient was a 79-year-old man who presented with a 3-year history of hyperglycemia and a 1-year history of polydipsia. At the time of presentation, he had been in a hypodynamic state for 15 days. Three years previously, he was diagnosed with impaired glucose tolerance without any symptoms, but no treatment was provided. One year earlier, he developed polydipsia, hyperuresis, and cutaneous pruritus, and lost weight. His random plasma glucose concentrations increased to as high as 20 mmol/L. Consequently, he was started on aspart 30 (21 units before breakfast and 8 units before dinner) and metformin (0.5 g twice a day). One month previously, he visited our hospital because of complaints of recurrent midnight hypoglycemia, particularly at approximately 02:00 am. During that period, although an insulin injection was gradually reduced and subsequently discontinued, his glucose concentration still dropped to 3 mmol/L. Laboratory tests showed that C-peptide and insulin concentrations were above the normal range, and the insulin autoantibody test was positive. At that time, non-classical IAS was considered as the probable cause of repeated hypoglycemia, and treatment was changed to acarbose (50 mg three times a day). After 15 days, blood tests showed the following: fasting plasma glucose level, 3.71 mmol/L; anti-insulin antibody, > 45.4 U/mL; and insulin concentrations were 1567.44/1493.06/1370.20/1616.43/1812.01 pmol/L at 0/30/60/120/180 min and C-peptide concentrations were 3.41/3.68/3.95/4.56/4.51 nmol/L at 0/30/60/120/180 min during the OGTT, respectively. For treatment of IAS, prednisone therapy was started at 12 mg daily (4 mg per dose three time daily) then reduced to 8 mg daily after 2 weeks and to 4 mg per night 1 week later. The diabetes treatment plan was changed to human biosynthetic insulin injection (16 units per day), sitagliptin (50 mg per day), and voglibose (0.3–0.2 mg twice a day). Repeated laboratory tests showed the following: C-peptide concentrations were 0.73/1.67 nmol/L at 0/2 h, respectively, and the insulin concentration was 728.14 pmol/L at 0 h during the OGTT. The glucose concentration fluctuated between 7 and 12.9 mmol/L.