Delayed onset Bickerstaff brainstem encephalitis overlapping Miller-Fisher Syndrome during SARS-CoV-2 infection

Bickerstaff brainstem encephalitis (BBE) is a neuroimmunologic disease characterized by the acute onset of external ophthalmoplegia, ataxia, and consciousness disturbance, mostly subsequent to an infection. BBE is considered to be a variant of Miller-Fisher syndrome (MFS), which also exhibits external ophthalmoplegia and ataxia but not presenting consciousness alterations. Therefore, these two medical conditions are included in the clinical spectrum of the "Fisher-Bickerstaff syndrome" ( Shahrizaila and Yuki in J Neurol Neurosurg Psychiatry 84(5):576-583) [1]. With regard to the etiopathogenesis, increasing evidence worldwide suggests that SARS-CoV-2 infection-enhanced immune response is involved in a wide range of neurological complications such as Guillain-Barré syndrome (GBS), MFS, acute necrotizing encephalitis (ANE), myelitis, acute disseminated encephalomyelitis (ADEM), and, although very rarely, BBE either (Hosseini et al. in Rev Neurosci 32:671-691) [2]. We report a case of a patient affected by delayed onset BBE overlapping MFS during a mild SARS-CoV-2 infection. To the best of our knowledge, similar cases have never been reported.