Interictal ocular motor findings in episodic ataxia type 2

This is a patient with CACNA1A-related episodic ataxia type 2 who initially presented with attacks of dizziness and ataxia. Over time, inter-ictal ocular motor abnormalities develop, which are seen in this video and commonly include gaze-evoked and rebound nystagmus. Although downbeat nystagmus (DBN) would be the most common spontaneous nystagmus, there is a downbeat component along with the gaze-evoked nystagmus in lateral gaze (the combination of which is referred to as "side pocket" nystagmus). Nevertheless, there's spontaneous upbeat nystagmus (UBN) instead of DBN. Given projections from brainstem vertical gaze holding pathways and nucleus of Roller and intercalatus to cerebellar flocculus, imbalance between pathways that are responsible for excitation or inhibition of central anterior semicircular canal pathways may cause DBN or UBN.