Frequency of anti-neural antibodies and autoimmune epilepsy in focal epilepsy of unknown etiology: An observational study in a Singaporean cohort.

Abstract

Objective: Autoimmune epilepsy (AES) is increasingly recognized as a condition in patients with epilepsy of unknown etiology. Early immunotherapy improves outcomes; however, data on its prevalence and the frequency of anti-neural/neuronal antibodies in Asian populations remain scarce. Herein, we aim to (1) evaluate the frequency of serum anti-neuronal/neural antibodies, (2) compare the clinical characteristics between seropositive and seronegative patients, and (3) explore the clinical utility of the ACES (Antibodies Contributing to Focal Epilepsy Signs and Symptoms) score in diagnosing AES in a cohort of Singaporean patients with focal epilepsy of unknown etiology.

Methods: This was a cross-sectional, observational, single-center study performed at the National Neuroscience Institute (NNI), Singapore. Patients with focal epilepsy of unknown etiology were prospectively recruited. Serum samples were tested using both cell-based (CBA) and immunohistochemistry (IHC)-based tissue assays. Patients were classified into definite, probable, and possible AES based on antibody positivity. Clinical characteristics, MRI and EEG findings, and ACES scores were analyzed.

Results: One-hundred-and-twenty patients were included. Nine patients (7.50%) were seropositive on IHC, while 2 patients (1.67%) were positive on CBA (1 with concomitant IHC positivity, 1 without). In total, 10 patients (8.33%) were seropositive on IHC and/or CBA. Seropositivity was associated with female sex, autoimmune and psychiatric comorbidities, behavioral changes, speech problems, abnormal MRI brain, medial temporal T2/FLAIR hyperintensities, and ACES ≥2. AUC of ACES for seropositivity was 0.878; sensitivity and specificity were 60.0% and 96.4% respectively at a cutoff of ≥2.

Significance: The frequency of specific, well-characterized anti-neural/neuronal antibodies in focal epilepsy of unknown etiology is low in Singapore. Distinct clinico-radiological features, in particular those that comprise the ACES score, were useful in identifying AES. Their presence should prompt antibody testing to confirm the diagnosis of AES for earlier immunotherapy.

Plain language summary: This study performed in Singapore investigated autoimmune epilepsy in people who have focal epilepsy with no clear cause. Researchers tested blood samples for antibodies linked to autoimmune epilepsy and compared clinical features between patients with and without these antibodies. Out of 120 patients, 10 had positive antibody tests-they were more often female, more likely to have autoimmune or psychiatric conditions, behavior or speech problems, and abnormal brain MRI findings. An ACES score of 2 or more was useful for identifying patients with antibodies. Using these clinical features can help clinicians decide who should be tested and treated earlier.