Abnormal Vertical Eye Movements as a Clue for Diagnosis of Niemann–Pick Type C

BACKGROUND: Adult-onset Niemann–Pick Type C is a rare neurogenetic lysosomal disorder, whose diagnosis is often delayed and missed because of its heterogeneous clinical presentations and rarity as well as the lack of awareness of characteristic eye findings among neurologists. PHENOMENOLOGY SHOWN: Impaired smooth pursuits, saccades, and optokinetic nystagmus in the vertical direction, with relatively normal eye movements in the horizontal direction, and ataxia features on finger chase testing, tandem walking, and gait ataxia. EDUCATIONAL VALUE: Impairment of vertical eye movements in combination with ataxia, cognitive impairment, and/or psychiatric symptoms in an adult patient should always raise clinical suspicion of Niemann–Pick Type C.