Central Vestibular Nystagmus in Anti-DPPX Encephalitis

This is a young woman who presented with oscillopsia due to spontaneous nystagmus in addition to gastrointestinal symptoms which led to the diagnosis of anti-DPP axis encephalitis. She was treated with rituximab, and experience gradual improvement over time. However, years after the onset, she continued to have spontaneous nystagmus in addition to oscillopsia. Seen here in the video is a spontaneous horizontal-torsional right beating nystagmus that was unidirectional in all directions of gaze, although increased in right gaze (in accordance with Alexander's law where nystagmus is more intense in the direction of the fast phase), stayed right beating and vertical gaze, and was even right beating in left gaze. This is a vestibular pattern of nystagmus, although there was no left sided vestibular loss to explain this right beating nystagmus. Therefore, this was a central vestibular nystagmus, and although there was no corresponding discrete lesion in the cerebellum or brainstem on her MRI, this was thought to be due to her previous encephalitis. Although smooth pursuit and vestibulo-ocular reflex suppression (VORS) were normal vertically as well as to the left, in the direction of the fast phase (to the right), pursuit and VORS appeared saccadic due to superimposed fast phases from her right-beating nystagmus.