Electroencephalographic findings in Bickerstaff's brainstem encephalitis: A possible reflection of the dysfunction of the ascending reticular activating system

Objectives: Bickerstaff's brainstem encephalitis (BBE) is a rare post-infectious inflammatory disease, which causes impaired consciousness by the dysfunction of the ascending reticular activating system (ARAS). We aimed to clarify EEG changes possibly caused by the dysfunction of the ARAS in BBE.

Methods: We retrospectively investigated 15 EEGs from 5 patients with definite BBE (i.e., the positivity for serum IgG anti-GQ1b antibodies was mandatory for the diagnosis) admitted to our hospital from January 2014 through December 2019, particularly focusing on whether N1 and N2 sleep patterns were maintained.

Results: All of the 10 EEGs recorded when patients had consciousness disturbance were abnormal. Stereotypical EEG changes correlating with their level of consciousness were identified: poorly organized posterior dominant rhythms with maintenance of sleep patterns in patients with mild consciousness disturbance (n = 5); predominant N1 and/or N2 sleep patterns even with external stimuli, including spindle coma pattern, in patients with moderate consciousness disturbance ("unarousable sleep-like" EEG) (n = 4); and generalized slow waves without N1 and N2 sleep patterns in patients with severe consciousness disturbance (n = 1). Among 5 patients, 3 (60%) had "unarousable sleep-like" EEG in their clinical course.

Conclusions: Patients with BBE showed stereotypical EEG changes correlating with their level of consciousness, mostly with maintenance of N1 and N2 sleep patterns, and often exhibited characteristic "unarousable sleep-like" EEG.

Significance: This study revealed characteristic EEG changes possibly caused by the dysfunction of the ARAS, which can be a diagnostic clue for BBE.