Behind the mask of relapsing bimodal encephalitis: herpesvirus 7 and Epstein-Barr virus associated with Hashimoto's encephalopathy: a case report.

BACKGROUND AND PURPOSE: Relapsing bimodal encephalitis in adults remains poorly characterized. We describe a case of relapsing viral encephalitis followed by secondary autoimmune-mediated encephalitis and explore its potential underlying mechanisms.

CASE DESCRIPTION: A previously healthy adult female initially presented with fever and headache; brain magnetic resonance imaging (MRI) showed punctate white matter hyperintensities, and electroencephalogram revealed background slowing with intermittent δ waves. Initial cerebrospinal fluid (CSF) analyses were suggestive of viral encephalitis. Although no pathogen was identified by CSF metagenomic next-generation sequencing (mNGS), she responded favorably to empirical antiviral therapy. 22 days after discharge, she was readmitted with decreased responsiveness, hypersomnia, and acute psychosis. Concurrent MRI revealed progressive white matter lesions. CSF analysis demonstrated oligoclonal bands restricted to the CSF, while autoimmune encephalitis antibody panels were negative. Serum autoantibodies (anti-SSA/SSB, anti-thyroglobulin, and thyroid peroxidase) were elevated. Considering probable autoimmune encephalitis, intravenous immunoglobulin and methylprednisolone were administered, leading to clinical and serological remission with radiological improvement. After 22 months, the patient relapsed with similar clinical manifestations, beginning with fever and headache, followed by decreased responsiveness, and subsequently developed an acute mental disorder. Repeat CSF mNGS detected human herpesvirus 7 (HHV-7) and Epstein-Barr virus (EBV), accompanied by new white matter lesions and recurrent thyroid autoantibodies. The patient responded favorably to the same treatment. At one-month follow-up, the patient developed hyperthyroidism.

CONCLUSION

HHV-7 and EBV with long latency are likely associated with a cascade of autoimmune encephalitis, presenting as relapsing bimodal encephalitis. Thyroid autoantibodies-rather than conventional neuronal antibodies-appear central to the autoimmune phase, consistent with Hashimoto's encephalopathy.