Gaze-Evoked, Rebound, and Centripetal Nystagmus in Cerebellar Degeneration

A 68-year-old female reported a 2-year history of progressive gait imbalance, falls, dizziness and vertical oscillopsia. She described that dizziness and oscillopsia were worst when looking down. There was no family history of ataxia. Composite gaze with fixation was recorded with video-oculography and demonstrated square wave jerks and spontaneous downbeat nystagmus (DBN) in primary gaze, and in lateral gaze, there was both DBN and gaze-evoked nystagmus (GEN) which created a down and lateral diagonal trajectory (so-called "side pocket" nystagmus). As is commonly seen with GEN, there was also rebound nystagmus when going from lateral to primary gaze (e.g. right beating-nystagmus in right gaze, changing to left-beating nystagmus upon return to primary gaze position). Additionally, after 5 seconds of sustained left gaze, nystagmus transitioned from centrifugal (slow phase drift towards primary position, with fast phase back towards the left, i.e. GEN causing left-beating nystagmus (LBN)) to centripetal nystagmus (slow phase drift towards the left, with fast phase back towards primary gaze) causing right-beating nystagmus (RBN). While there was no obvious centripetal nystagmus in right gaze during this recording, the GEN did slow down and likely would have transitioned to centripetal (LBN) had this position been held for a longer period of time. GEN is a common feature of cerebellar disease and occurs due to impaired function of the neural integrators (key structures of which include the nucleus prepositus hypoglossi and medial vestibular nucleus for horizontal gaze-holding, and the interstitial nucleus of Cajal for vertical and torsional gaze-holding), with connections to the flocculus/paraflocculus of the cerebellum to refine and improve neural integrator function (1). With GEN, compensatory mechanisms attempt to minimize the slow phase drift back toward primary position, and this compensatory bias will shift the resting position of the eyes more eccentrically (2). Ideally, this shift in the null region should be balanced with the slow phase drift back to center. Imbalance between compensatory and pathological biases can create its own slow phase drift. In the case of rebound nystagmus, if the patient looks to the left, in an effort to minimize the rightward slow phase drift back toward center, compensatory mechanisms will pull the null region farther out to the left. When the patient looks from left to straight ahead gaze, the now right-beating (rebound) nystagmus is akin to a GEN and continues until the compensatory and pathological biases are in equipoise (1, 2). Similarly, centripetal nystagmus probably represents a compensatory shift in the null region farther to the left as compared to the actual eye position in left gaze, the result being a leftward slow phase drift followed by a centripetal fast phase. Thus, the appearance of centripetal nystagmus may represent an over-compensation, usually brought on by sustained (>10 seconds) eccentric gaze (1). In this patient, other ocular motor signs of cerebellar degeneration evident on exam included moderately saccadic smooth pursuit and vestibulo-ocular reflex suppression, and apogeotropic nystagmus in right and left Dix-Hallpike and supine roll testing (central in origin rather than due to horizontal canal benign paroxysmal positional vertigo). The etiology of her cerebellar degeneration has remained idiopathic. See additional video: https://collections.lib.utah.edu/ark:/87278/s62pby9e