Nystagmus in Superior Cerebellar Artery Infarcts — A Paradigm Shift
January 1, 2013 4 minutes read
Nystagmus in Superior Cerebellar Artery Infarcts — A Paradigm Shift
Abstract & Commentary
By Marc Dinkin, MD, Assistant Professor of Ophthalmology, Weill Cornell Medical College. Dr. Dinkin reports no financial relationships relevant to this field of study.
Synopsis: Video-oculography reveals spontaneous or gaze-evoked nystagmus in more than a quarter of patients with isolated superior cerebellar infarction.
Source: Lee H, Kim AH. Nystagmus in SCA territory cerebellar infarction: Pattern and a possible mechanism. J Neurol Neurosurg Psychiatry 2012; Nov 20 [Epub ahead of print].
Nystagmus is a to-and-fro movement of the eyes in which the first phase of the movement is slow and is followed by a corrective movement that is either slow (pendular) or fast (jerk). It frequently results from an imbalance in the otolithic inputs governing the vestibular ocular reflex or to injury to its central mediators, which include the medial vestibular nucleus and flocculus of the cerebellum. The presence and features of nystagmus in the patient with acute vestibular syndrome provide important clues to the localization of the condition: Diseases affecting the labyrinth or vestibular nerve typically cause a unidirectional spontaneous nystagmus (SN) that ameliorates with fixation, while central nystagmus localizing to the brainstem and cerebellum is direction-changing and is not affected by fixation.
Until now, the prevailing notion has been that nystagmus occurs with inferior cerebellar infarcts due to floccular-nodular injury, associated with either posterior inferior cerebellar artery or anterior inferior cerebellar artery occlusion. Isolated rostral cerebellar infarcts due to superior cerebellar arteries (SCA) occlusion lead to ataxia and dysarthria, but in the absence of brainstem involvement, vestibular nystagmus has not been well-described. In a recent study published in the Journal of Neurology, Neurosurgery and Psychiatry, Lee and colleagues challenged this dogma with a study of eye movements in patients with isolated SCA-territory infarcts.
Using MRI, the authors selected 41 patients whose strokes were in the territory of the SCA. The head impulse test was negative for all, ostensibly ruling out any contribution by a peripheral process. Video-oculography was used to record the direction and intensity of SN, both with and without fixation, and gaze-evoked nystagmus (GEN). Finally, the overlapping regions of infarct on MRI in the non-nystagmus group were subtracted from those in the nystagmus group to determine a putative anatomical basis for nystagmus in these patients.
Surprisingly, a majority (63.6%) of patients complained of vertigo at presentation, and 27% demonstrated some form of nystagmus, although resolution occurred within a week in 80% of them. Out of 11 patients with nystagmus, SN was present in 10 and GEN was present in five. The SN was horizontal in 80%, in which case it beat toward the lesion side, and was attenuated by fixation, a feature typically reserved for peripheral nystagmus. Four of the five patients with direction-changed bidirectional GEN also had SN. The maximum overlap region included the ala (wing) of the central lobule and the most anterior parts of the quadrangular lobule, both part of the rostral anterior cerebellum.
Commentary
These results provide new insights into the functions of the superior cerebellum, and challenge the conventional wisdom that superior cerebellar injury does not produce a vestibular syndrome. The authors speculate that SCA infarcts may remove rostral-anterior cerebellar hemisphere inhibition of the fastigial nucleus, allowing it to overstimulate the ipsilateral medial vestibular nucleus, resulting in a slow phase away from the lesion and the ipsilesional jerk nystagmus observed in this study and in some animal studies. This helps explain why visual fixation might ameliorate this SN as it does peripheral nystagmus, since both conditions ultimately result from an imbalance of medial vestibular nucleus tone. Of course, another possibility is that this SN really did reflect a peripheral etiology, such as might occur with transient labyrinthine ischemia. At one point, the authors argue that the normal head impulse test essentially ruled that out, while in another paragraph, they concede that the test might be negative in the case of transient labyrinthine ischemia. Certainly if we are to consider the possibility of amelioration with fixation in a central lesion, then we might also consider a negative head impulse test in some cases of peripheral dysfunction.
The presence of GEN is attributed to transient ischemia to the neural integrator housed in part by the vestibulocerebellum, a notion that is supported by the evanescence of the GEN in these patients. This conclusion is logical given the lack of known circuitry in the superior cerebellum that would produce GEN. If it is correct, however, the implicit conclusion is that the SN observed in most of the same patients also resulted from transient inferior cerebellar ischemia rather than through the theoretical scheme discussed above.
Regardless of the exact anatomical basis for these findings, this article provides an important contribution to our approach to patients with nystagmus, as we are cautioned not to rule out a central cause of acute vertigo just because the associated SN improves with fixation. Larger studies, preferably with the clinicians who review the eye movement recordings blinded to the results of the MRIs, would help confirm their results, as would functional MRI and tractography studies focused on the superior cerebellum, but for now it is safe to say that there may be more to our understanding of cerebellar modulation of vestibular function than meets the eye.
Video-oculography reveals spontaneous or gaze-evoked nystagmus in more than a quarter of patients with isolated superior cerebellar infarction.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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