Brainstem Encephalitis Following COVID-19 Vaccination: A Case Report.

Encephalitis is an extremely rare neurological adverse event following vaccination against coronavirus disease 2019 (COVID-19). We report a case of brainstem encephalitis following mRNA COVID-19 vaccination. A 30-year-old Japanese female presented with acute diplopia characterized by recurrent, paroxysmal episodes following the second dose of the vaccine, which resolved spontaneously. Brain magnetic resonance imaging revealed inflammatory changes in the brainstem. The patient responded rapidly to steroid therapy and subsequently improved. This case shares key clinical features with another case, including similarities in symptoms, lesion localization, and steroid responsiveness. However, it differs with respect to the timing of symptom onset and the presence of mild residual deficits. This report makes a contribution to the limited literature on this rare post-vaccination condition by documenting its clinical features.