Autoimmune encephalitis-associated epilepsy with glutamic acid decarboxylase autoantibodies and type 1 diabetes mellitus: A comprehensive systematic scoping review of a clinical syndrome

BACKGROUND: Type 1 diabetes mellitus (T1DM) and autoimmune neurological syndromes (AINS), including autoimmune encephalitis-associated epilepsy/seizures (AEAE/S), share immune-mediated mechanisms linked to glutamic acid decarboxylase-65 autoantibodies (GAD-AABs). We reviewed features of patients with the syndrome of coexisting GAD-AAB-associated T1DM and AEAE/S. METHODS: According to PRISMA-ScR, English studies from PubMed, Web of Science, and Scopus were reviewed for patients with T1DM, AEAE/S, and GAD-AABs. RESULTS: We included 78 patients (64% female) from 50 studies. Age at first presentation ranged from 1 to 72 years [25.6 (±17.07)]. T1DM preceded AEAE/S in 40% (n = 31), followed it in 29% (n = 23), overlapped in 9% (n = 7), and unknown order in 22% (n = 17). GAD-AABs were detected in serum in 77/78 patients, and in CSF in 41/60 tested (68%). Brain MRI was abnormal in 41/54 cases (76%), mostly temporal T2-FLAIR hyperintensity (n = 25; 46%). EEG showed interictal epileptiform discharges in 42/51 (82%) and ictal patterns in 19 (37%). Autoimmune thyroid disorders (n = 33; 42%) and overlapping AINS (n = 13; 17%) were frequent. Antiseizure medication was reported in 46 cases (59%), and drug resistance in 32/46 (70%). Of 68 cases with data, 50 (73.5%) received immunotherapy, mainly intravenous immunoglobulins and corticosteroids. Follow-up showed variable seizure control, psycho-cognitive symptoms in 22%, and two deaths. CONCLUSION: The syndrome of GAD-AAB-associated AEAE/S + T1DM exhibits age-dependent variations in clinical presentation with predominantly focal temporal seizures. People with T1DM should be screened for AINS, and those with AEAE/S for autoimmune (endocrine) disorders. A comprehensive immunological assessment guides diagnosis and targeted therapy.