Autoimmune encephalitis: new hammers in the toolbox

Mesiotemporal Volumetry, Cortical Thickness, and Neuropsychological Deficits in the Long-term Course of Limbic Encephalitis

BACKGROUND AND OBJECTIVES

Limbic encephalitis (LE) is an autoimmune disease often associated with temporal lobe epilepsy and subacute memory deficits. It is categorized into serologic subgroups, which differ in clinical progress, therapy response, and prognosis. Using longitudinal MRI analysis, we hypothesized that mesiotemporal and cortical atrophy rates would reveal serotype-specific patterns and reflect disease severity.

METHODS

In this longitudinal case-control study, all individuals with antibody-positive (glutamic acid decarboxylase 65 [GAD], leucine-rich glioma-inactivated protein 1 [LGI1], contactin-associated protein 2 [CASPR2], and N-methyl-d-aspartate receptor [NMDAR]) nonparaneoplastic LE according to Graus' diagnostic criteria treated between 2005 and 2019 at the University Hospital Bonn were enrolled. A longitudinal healthy cohort was included as the control group. Subcortical segmentation and cortical reconstruction of T1-weighted MRI were performed using the longitudinal framework in FreeSurfer. We applied linear mixed models to examine mesiotemporal volumes and cortical thickness longitudinally.

RESULTS

Two hundred fifty-seven MRI scans from 59 individuals with LE (34 female, age at disease onset [mean ± SD] 42.5 ± 20.4 years; GAD: n = 30, 135 scans; LGI1: n = 15, 55 scans; CASPR2: n = 9, 37 scans; and NMDAR: n = 5, 30 scans) were included. The healthy control group consisted of 128 scans from 41 individuals (22 female, age at first scan [mean ± SD] 37.7 ± 14.6 years). The amygdalar volume at disease onset was significantly higher in individuals with LE (p ≤ 0.048 for all antibody subgroups) compared with that in healthy controls and decreased over time in all antibody subgroups, except in the GAD subgroup. We observed a significantly higher hippocampal atrophy rate in all antibody subgroups compared with that in healthy controls (all p ≤ 0.002), except in the GAD subgroup. Cortical atrophy rates exceeded normal aging in individuals with impaired verbal memory, while those who were not impaired did not differ significantly from healthy controls.

DISCUSSION

Our data depict higher mesiotemporal volumes in the early disease stage, most likely due to edematous swelling, followed by volume regression and atrophy/hippocampal sclerosis in the late disease stage. Our study reveals a continuous and pathophysiologically meaningful trajectory of mesiotemporal volumetry across all serogroups and provides evidence that LE should be considered a network disorder in which extratemporal involvement is an important determinant of disease severity.

Autoimmune Encephalitis

Autoimmune encephalitis is a common and treatable cause of encephalitis in children and adults. Individuals present with a variety of symptoms, including altered mental status, behavioral changes, irritability, insomnia, developmental regression, seizures, dyskinetic movements, and autonomic instability. Evaluation includes electroencephalography, magnetic resonance imaging, and lumbar puncture. Once infectious and other causes are reasonably ruled out, treatment should be started empirically without waiting for antibody confirmation. Early clinical suspicion is key, as the outcome depends on early initiation of immunotherapy, including corticosteroids, intravenous immunoglobulin, and/or plasmapheresis. Severe or refractory cases require other treatments, such as rituximab, cyclophosphamide, or other immunotherapies using novel monoclonal antibodies. Psychiatry should be involved early for the management of behavioral issues. Additional considerations include management of seizures and dyskinesias. ICU admission may be required for management of hypoventilation necessitating mechanical ventilation (either intrinsic or iatrogenic, eg, from sedatives), refractory seizures, and dysautonomia. Anti-N-methyl-d-aspartate receptor and other forms of autoimmune encephalitis are less often associated with neoplasia (such as ovarian teratoma) in children compared with adults, but screening and removal of tumor if present should be performed.