[A case of brain stem encephalitis with bilateral horizontal gaze palsy]

A 41-year-old woman developed horizontal diplopia and difficulty in moving her eyes. On neurological examination, her eyes showed absolute bilateral horizontal gaze palsy, but convergency and vertical eye movement were normal. The cerebrospinal fluid findings revealed an increased IgG level and myelin basic protein. T2-weighted magnetic resonance imaging revealed a high-signal-intensity area in the lower pontine tegmentum affecting bilateral horizontal gaze. We diagnosed her as having brain stem encephalitis based on the above data. After 1.5 months of corticosteroid treatment, bilateral horizontal palsy disappeared completely. Several cases showing bilateral horizontal gaze palsy have been reported, but few have involved absolute bilateral horizontal gaze palsy caused by brain stem encephalitis.