Steroid-Refractory Insulin Autoimmune Syndrome Treated With Rituximab and Continuous Glucose Monitoring

A 67-year-old female presented with severe hypoglycemia with a blood glucose of 34 mg/dl five hours after having dinner. She did not have diabetes and had no access to oral hypoglycemic agents, insulin, or any other drug known to cause hypoglycemia. She was a known case of primary hypothyroidism euthyroid on treatment. The physical examination was unremarkable. Her liver, renal functions, thyroid, and adrenal functions were normal. At a blood sugar level of 23 mg/dl, her serum insulin was 24,000 uU/ml (normal: <3 uU/ml) and C-peptide was 16.2 ng/ml (normal: 0-0.6 ng/ml), which were were very high. As the serum insulin levels were very high, insulin autoimmune syndrome (IAS) was suspected. Insulin autoantibodies (IAAs) were positive [87.2 units/ml (normal: <12)]. Imaging with contrast-enhanced CT (CECT) of the abdomen, endoscopic ultrasonography, and 68 gallium octreotide DOTANOC whole-body PET-CT scan did not reveal any pancreatic or extra-pancreatic tumor. Eventually, the patient was diagnosed with IAS. She was started on high-dose prednisolone, diazoxide, and octreotide in addition to low carbohydrate meals. Hypoglycemic episodes continued for one month despite this therapy. Remission was achieved only after two doses of rituximab 1 g IV infusion were given. Serum insulin levels decreased to 230 uU units from 24,000 uU/ml, and the patient's hypoglycemic and hyperglycemic episodes were normalized. We used continuous glucose monitoring with the FreeStyle Libre glucose monitoring system, and the management of the patient was greatly facilitated by this.