A Case Report of Anti-GAD65 Antibody-Positive Autoimmune Encephalitis Associated with Diabetes

BACKGROUND: Patients with GAD65 antibody-associated autoimmune encephalitis who also have diabetes are usually considered to have type 1 diabetes mellitus (T1DM). However, previous reports often lacked β-cell function assessments, relying solely on anti-GAD65 positivity for diagnosis, which is insufficient for accurate classification. CASE PRESENTATION: We present a 30-year-old Chinese woman diagnosed with GAD65-associated autoimmune encephalitis, hyperthyroidism, and diabetes. Her peak C-peptide level was 3.99 ng/mL, inconsistent with the β-cell dysfunction typical of classic T1DM. The combination of high GAD65 antibody titers and preserved β-cell function made it challenging to determine her diabetes type. CONCLUSION: This case suggests that clinicians should pay more attention to assessing and monitoring β-cell function when GAD65-associated autoimmune encephalitis is accompanied by diabetes.