Insulin autoimmune syndrome (IAS) is a rare condition that can be overlooked in the differential diagnosis of hypoglycemia. Hematologic malignancies such as multiple myeloma (MM) have been associated with IAS. Very few cases of IAS due to multiple myeloma have been reported in the literature. We wanted to present our case who applied to our clinic with severe hypoglycemia and was diagnosed with multiple myeloma-associated IAS.

An 83-year-old male patient was admitted to our clinic with recurrent severe hypoglycemia episodes. When the patient’s plasma glucose was 37 mg/dL, insulin level was high (2266 µIU/ml), C-peptide level was relatively normal (3.44 ng/ml); cortisol and ACTH levels were also normal. No pathologic finding was detected in the abdominal MRI and Ga-68 PET/CT. Anti-insulin antibody (IAA) was tested for IAS, and the antibody level was found to be 95.9%. The patient was evaluated in terms of possible conditions that may lead to IAS. Hematology consultation was made due to the fact that the patient had anemia, chronic renal failure, and albumin/globuline discordance, and he was diagnosed with IgG kappa multiple myeloma. Bortezomib and dexamethasone treatment was initiated. A decrease in hypoglycemic symptoms was observed with chemotherapy.

IAS should be considered in the differential diagnosis of recurrent hypoglycemia cases of unknown cause. It should be kept in mind that IAS may develop due to multiple myeloma, especially in patients with advanced age and anemia.