Acute and longitudinal magnetic resonance imaging abnormalities in antibody-mediated encephalitis

Brain magnetic resonance imaging (MRI) abnormalities are an important finding in the evaluation of patients with suspected autoimmune encephalitis (AE). There have been few studies evaluating the frequency and prognostic significance of MRI abnormalities, especially hippocampal swelling, in anti-N-methyl-D-aspartate receptor (NMDAR) and anti-leucine-rich glioma-inactivated 1 (LGI1) Ab-mediated encephalitides. We conducted a multi-centre, retrospective study involving adult patients with confirmed antibody-mediated encephalitis and at least one MRI scan from 10 Australian hospitals (n = 139). MRI scans were evaluated by a neuroradiologist blinded to the specific autoimmune encephalitis diagnosis. We evaluated associations between acute MRI abnormalities (e.g. hippocampal swelling) with 12-month function (modified Rankin scale, mRS ≥2 = worse outcome) and radiological findings. In patients with anti-LGI1 Ab-mediated encephalitis, we identified hippocampal swelling on initial MRI to be associated with worse function at 12 months (OR 0.03; 95% CI 0.003, 0.34; P = 0.005). We found initial AE-associated T2/fluid attenuated inversion recovery (FLAIR) hyperintensities were not associated with 12-month mRS in either the anti-NMDAR (OR 0.39; 95% CI 0.04, 3.97; P = 0.42) or anti-LGI1 Ab-mediated encephalitis groups (OR 0.34; 95% CI 0.07, 1.57; P = 0.17). In anti-LGI1 Ab-mediated encephalitis, both hippocampal swelling (OR 5.76; 95% CI 1.14, 29.02; P = 0.03) and T2/FLAIR hyperintensity (OR 6.81; 95% CI 1.28, 36.22; P = 0.03) were related to the development of mesial temporal atrophy and hippocampal sclerosis. Acute hippocampal swelling is associated with worse outcomes in anti-LGI1 Ab-mediated encephalitis and, alongside initial T2/FLAIR hyperintensity, is associated with the development of both mesial temporal atrophy and hippocampal sclerosis.