Are signs of ocular tilt reaction in patients with cerebellar lesions mediated by the dentate nucleus?

Objective: A sensitive clinical sign of a vestibular tone imbalance in the roll plane is the ocular tilt reaction (OTR), a combination of head and perceptual tilts, vertical divergence of the eyes (skew deviation, SD) and ocular torsion (OT) in the same direction. While these signs are regularly seen in patients with acute unilateral brainstem lesions affecting central vestibular pathways, only a few case studies are available on its occurrence in patients with cerebellar lesions[1,2]. Thus, the question arises whether contra- and/or ipsiversive tilts of the perceived vertical and the other signs of OTR, such as SD and OT can be found in pure cerebellar lesions and if so, which cerebellar structures may be involved. Methods: We used lesion mapping technique in MRI and CT in a total of 31 patients with acute circumscribed cerebellar strokes all showing a significant tilt of the perceived subjective visual vertical (SVV). Twenty-three patients had a contraversive tilt of the SVV; they were compared to 8 patients with ipsiversive tilts of the SVV. Both groups were comparable with respect to age, acuteness of lesion, size of lesion, and the occurrence of additional central ocular motor symptoms such as OT and SD. In an additional analysis we further compared the lesions of the two subgroups with contra- and ipsiversive OT, SD and head tilt. Result: MRI/CT lesion mapping revealed that in patients showing contraversive signs of OTR in general and contraversive SVV tilts in particular the dentate nucleus was the commonly damaged structure independent of head tilts. Ipsiversive signs of OTR were associated with lesions of the biventer lobule, the middle cerebellar peduncle, the tonsil, and the inferior semilunar lobule. Conclusion: Our data give evidence that OTR is a common sign in patients with pure unilateral cerebellar lesions. Therefore, OTR can not only indicate acute unilateral brainstem or peripheral vestibular lesions but also cerebellar lesions. Furthermore, these data suggest that the dentate nucleus is the critical anatomical structure within the cerebellum belonging to a network involved in the perception of verticality. A lesion of the dentate nucleus causes tilts of the SVV in the contraversive direction, i.e., a vestibular tone imbalance to the contralateral side, whereas cerebellar lesions excluding the dentate nucleus induced a tone imbalance to the ipsilesional side. Literatur: [1] Neurology 1997;49:491–493. [2] Neuro-ophthalmology 1999;22:81–85.