Autoimmune Encephalitis Concomitant with SARS-CoV-2 Infection: Insight from 18F-FDG PET Imaging and Neuronal Autoantibodies

Abstract

We report the case of a 72-y-old man with concomitant autoimmune encephalitis and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The patient presented with subacute cerebellar syndrome and myoclonus several days after general infectious symptoms began. Methods: Clinical examination, CT, PET, MRI, and autoantibody testing were performed. Results: The oropharyngeal swab test was positive for SARS-CoV-2. The brain MRI results were normal. Cerebrospinal fluid testing showed normal cell counts, a negative result on reverse-transcription polymerase chain reaction testing, and no oligoclonal banding. Brain ¹⁸F-FDG PET showed diffuse cortical hypometabolism associated with putaminal and cerebellum hypermetabolism, compatible with encephalitis and especially cerebellitis. The immunologic study revealed high titers of IgG autoantibodies in serum and cerebrospinal fluid directed against the nuclei of Purkinje cells, striatal neurons, and hippocampal neurons. Whole-body ¹⁸F-FDG PET and CT scans did not show neoplasia. Treatment with steroids allowed a rapid improvement in symptoms. Conclusion: This clinical case argues for a possible relationship between SARS-CoV-2 infection and autoimmune encephalitis and for the use of ¹⁸F-FDG PET in such a context.

Keywords: 18F-FDG PET; COVID-19; SARS-CoV-2; autoimmune encephalitis; methylprednisolone.

FIGURE 1.

¹⁸F-FDG brain, whole-body PET, and brain MRI findings. (A and B) Brain ¹⁸F-FDG PET sagittal and axial slices showing diffuse cortical hypometabolism associated with putaminal and cerebellum hypermetabolism (A), confirmed by SPM comparison to 20 healthy elderly subjects (B) (P < 0.001, k > 600). (C and D) Whole-body ¹⁸F-FDG PET/CT showing slight lung and hilar lymph node hypermetabolism on maximum-intensity projection (C) and axial fused slices (D), matching pseudonodular retractile consolidation postinfectious findings on CT, without straightforward argument for neoplasia. (E) Axial slices from T2-weighted fluid-attenuated inversion recovery MRI of putamen and cerebellum showing no abnormalities.

FIGURE 2.

Immunostaining of neuronal nuclei; 25-μm sections were obtained from frozen rat nerve tissue and incubated with different dilutions of serum or CSF and peroxidase-labeled anti-IgG antisera. Immunostaining was revealed in presence of 3-amino-9-ethylcarbazole. This NDP.view2 (Hamamatsu) figure shows labeling with CSF diluted to one sixth on nuclei of Purkinje cells in cerebellum, as well as striatal and hippocampal neurons.