Autoimmune Encephalitis After SARS-CoV-2 Infection: Case Frequency, Findings, and Outcomes

Abstract

Background and objectives: Autoimmune encephalitis (AE) cases after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection have been reported, but the frequency is unknown. We aimed to determine the frequency and diagnostic features of coronavirus disease 2019 (COVID-19)-related AE.

Methods: Residual sera from 556 consecutive Mayo Clinic Rochester patients (laboratory cohort) who underwent autoimmune encephalopathy neural immunoglobulin G (IgG) evaluation were tested for total antibodies against the SARS-CoV-2 spike glycoprotein using a Food and Drug Administration-authorized chemiluminescence assay (October 2019-December 2020). Clinical records from patients with a positive SARS-CoV-2 antibody result and available research consent were reviewed. This laboratory cohort was cross-referenced with the Department of Neurology's COVID-19-related consultative experience (encephalopathy cohort, n = 31).

Results: Eighteen of the laboratory cohort (3%) were SARS-CoV-2 antibody positive (April-December 2020). Diagnoses were as follows: AE, 2; postacute sequelae of SARS CoV-2 infection (PASC), 3; toxic-metabolic encephalopathy during COVID-19 pneumonia, 2; diverse non-COVID-19 relatable neurologic diagnoses, 9; unavailable, 2. Five of the encephalopathy cohort had AE (16%, including the 2 laboratory cohort cases that overlapped), representing 0.05% of 10,384 patients diagnosed and cared for with any COVID-19 illness at Mayo Clinic Rochester in 2020. The 5 patients met definite (n = 1), probable (n = 1), or possible (n = 3) AE diagnostic criteria; median symptom onset age was 61 years (range, 46-63); 3 were women. All 5 were neural IgG negative and 4 tested were SARS-CoV-2 PCR/IgG index negative in CSF. Phenotypes (and accompanying MRI and EEG findings) were diverse (delirium [n = 5], seizures [n = 2], rhombencephalitis [n = 1], aphasia [n = 1], and ataxia [n = 1]). No acute disseminated encephalomyelitis cases were encountered. The 3 patients with possible AE had spontaneously resolving syndromes. One with definite limbic encephalitis was immune therapy responsive but had residual mood and memory problems. One patient with probable autoimmune rhombencephalitis died despite immune therapy. The remaining 26 encephalopathy cohort patients had toxic-metabolic diagnoses.

Discussion: We encountered occasional cases of AE in our 2020 COVID-19 experience. Consistent with sporadic reports and small case series during the COVID-19 pandemic, and prior experience of postinfectious AE, our cases had diverse clinical presentations and were neural IgG and CSF viral particle negative. Application of diagnostic criteria assists in differentiation of AE from toxic-metabolic causes arising in the setting of systemic infection.

Figure 1. Laboratory and Encephalopathy Cohorts and Numbers of Autoimmune Encephalitis (AE) Cases

+ve = SARS-CoV-2 antibody positive; Ab = antibody; COVID-19 = coronavirus disease 2019; PASC = postacute sequelae of SARS-CoV-2 infection; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.

Figure 2. Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Serum Antibody Results Between November 2019 and December 2020

Figure 3. Three Patients With Autoimmune Encephalitis (AE) After Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection With Abnormal Brain MRI

All axial T2 fluid-attenuated inversion recovery brain images (none had enhancement on T1 postgadolinium). (A) Patient 1, volume loss of both hippocampi, 6 weeks after onset of cognitive impairment and seizures. (B–D) Patient 2, hazy, diffuse T2 hyperintensity of the medulla (B), bilateral dentate (C), periventricular white matter, and posterior internal capsule (D). (E, F) Patient 4, T2 hyperintensities in the bilateral middle cerebellar peduncles (E) extending to the pons (F).