Objective: Describe a patient with persistent downbeat nystagmus(DBN) related to Arnold-Chiari type I malformation

Background: As a rare acquired nystagmus with various causes, DBN is a strong sign localizing the causative lesion to the posterior fossa, but the pathogenesis is still not fully disclosed.

Methods: We reported a persistent DBN case presenting with oscilopia and imbalance. MRI scan was performed and the drug treatment response was followed up.

Results: A 66-year old woman presented with episodic oscillopsia and imbalance on walking one year prior admission. Intermittent dizziness and suboccipital headache appeared when she was 20 years old. Neurological examination revealed spontaneuous DBN, which appeared in the primary position of the eyes, and increased on downward and lateral and gaze. MRI disclosed her¬niation of the cerebellar tonsils through the foramen magnum with compression of the caudal brain-stem, confirming Arnold-Chiari type I malformation. After taking GABA agonists, dizziness was partially improved, but DBN was persistent.

Conclusions: Compression of the herniating cerebellum against the caudal brain-stem resulting in a disinhibition of the superior vestibular neucleus, may explain the persistent DBN in this patient with Chiari malformation. Drug response was poor to this congenital disease.

References: 1. Pierrot-Deseilligny C, Milea D. Vertical nystagmus: clinical facts and hypotheses. Brain. 2005;128:1237–1246. 2. Spooner JW, Baloh RW. Arnold-Chiari malformation: improvement in eye movements after surgical treatment. Brain. 1981;104:51–60.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/persistent-downbeat-nystagmus-due-to-arnold-chiari-type-i-malformation/