Antineuronal antibody titres in autoimmune encephalitis: clinical implications for diagnosis and long-term immunotherapy.

INTRODUCTION

The role of antineuronal antibody titres in the acute and long-term diagnostic and therapeutic management of autoimmune encephalitis (AE) remains unclear. In this retrospective monocentric cohort study, we aimed to (I) identify specific characteristics in antibody testing distinguishing AE from non-AE patients, (II) evaluate the prognostic significance of antineuronal antibody findings and (III) assess outcomes and long-term immunotherapy in patients with AE.

METHODS

Patients with suspected autoimmune-associated neuropsychiatric conditions underwent antineuronal antibody testing between 01/2017 and 03/2023. Patients with positive antibody tests were stratified into AE and non-AE groups based on the clinical criteria proposed by Graus and colleagues. Long-term outcomes, antibody titres, and therapeutic strategies were analysed in AE patients over a three-year follow-up period. Among 2,466 patients tested, 53 met the diagnostic criteria for AE.

RESULTS

In AE patients with paired serum and CSF samples (n = 44), antibodies were detectable in both serum and CSF in 55% of cases (n = 24), in serum only in 36% (n = 16), and in CSF only in 9% (n = 4). AE patients with poor outcomes (n=5) showed a trend toward higher median CSF titres in the acute phase and at four months post-onset compared to patients with good outcomes (n=14); however, differences were not statistically significant. Regarding long-term immunotherapy, rituximab-treated patients experienced fewer relapses than those receiving intravenous-immunoglobulins (IVIG; p-value = 0.02).

DISCUSSION: These exploratory results from a small, heterogeneous cohort require confirmation in larger, prospective studies. Based on our data regarding serum and CSF antibodies, in a resource- limited setting we propose a stepwise diagnostic approach starting with serum screening; in suspected anti-NMDAR-AE, initial paired serum/CSF testing remains essential. If antibodies are detected in serum, additional CSF antibody testing may provide diagnostic confirmation and help guide treatment decisions, as high acute-phase CSF titres may suggest poorer long-term outcomes; however, this potential prognostic value requires confirmation in larger, antibody-specific studies.