Transient Anti-Glutamic Acid Decarboxylase (GAD) Antibody Positivity and Insulin Secretion Reduction After IVIg in Type 2 Diabetes Mellitus.

This report describes a patient with type 2 diabetes mellitus who received intravenous immunoglobulin therapy for Guillain-Barré syndrome and subsequently experienced a sudden deterioration in glycemic control. Although anti-glutamate decarboxylase antibodies became positive and insulin secretion was transiently suppressed, both findings returned to baseline during the follow-up period. These changes initially raised concerns about new-onset or coexisting type 1 diabetes mellitus; however, the reversibility of anti-glutamate decarboxylase antibody positivity and the eventual restoration of insulin secretion argued against a new or evolving form of autoimmune diabetes. In type 2 diabetes, chronic inflammation may predispose individuals to immune dysregulation, and receiving intravenous immunoglobulin could transiently exacerbate underlying metabolic instability. In this case, however, the marked hyperglycemia and the brief period of suppressed insulin secretion did not lead to sustained autoimmune activity or permanent β-cell dysfunction. Instead, the patient's anti-glutamate decarboxylase levels reverted to normal, insulin production capacity improved, and classification as type 2 diabetes mellitus was ultimately reaffirmed. These findings underscore the need for clinicians to remain vigilant when interpreting new-onset antibody positivity or metabolic disturbances that arise shortly after intravenous immunoglobulin therapy. Repeated assessment of both antibody levels and insulin secretion is crucial to avoid premature changes in diabetes classification or therapeutic strategies based solely on transient antibody elevation. This case highlights the importance of recognizing that anti-glutamate decarboxylase antibody positivity and corresponding hyperglycemia can be induced transiently by immunoglobulin therapy and do not necessarily indicate progression to type 1 diabetes mellitus. Regular monitoring of metabolic parameters and clinical status over time can ensure more accurate diagnosis and management in patients with preexisting diabetes who experience sudden, unexplained changes in blood glucose following immunoglobulin administration.