Lateropulsion

This 60 year old patient has Wallenberg's syndrome due to infarction of the left dorsolateral medulla. Wallenberg's syndrome is the best recognized syndrome involving the vestibular nuclei and adjacent structures. Unilateral infarcts affecting the vestibular nuclei may produce an oculomotor imbalance manifest by: 1.Spontaneous nystagmus 2.Skew deviation 3.Ocular tilt reaction (OTR) An additional finding - lateropulsion (deviation of the eyes towards the side of the lesion) may occur in darkness, behind closed lids, or with a blink, as in this case. Lateropulsion of saccades may reflect interruption of axons running in the inferior cerebellar peduncle from the inferior olivary nucleus to the cerebellum. Figure 1 shows a hypothetical scheme to account for lateropulsion of saccades. Interruption of climbing fibers originating from the inferior olivary nucleus may occur prior to their crossing in the medulla (1) or as they enter the inferior cerebellar peduncle in Wallenberg's syndrome. (2) Loss of climbing fiber inputs to Purkinje cells in the dorsal vermis causes the latter to inhibit the fastigial nucleus (4), which causes ipsipulsion of saccades. Pharmacological inactivation of the dorsal vermis (3) causes contrapulsion (although clinical lesions produce bilateral hypometria). Interruption of crossed fastigial nucleus outputs in the superior cerebellar peduncle (uncinate fasciculus, (5) causes contrapulsion. Thus contrapulcsion arises at sites 1, 3 and 5 and ipsipulsion at sites 2 and 4. Taken from Leigh RJ, Zee DS. The Saccadic System. Chp 3; 108-187. In: The Neurology of Eye Movements 4th Edition. Oxford University Press, New York 2006 with permission. Also consistent with this scheme is the observation that ipsipulsion of saccades with deviation of the eyes to the side of the lesion can be produced experimentally by lesions of the fastigeal nucleus. For further review of lateropulsion, nystagmus and the OTR see Box 12-1 Ocular Motor Findings in Wallenberg's Syndrome of Dorsolateral Medullary Infarction. Pg. 603 (8). View also ID161-20 - a patient with lateropulsion and multiple sclerosis alongside this case. See also: http://content.lib.utah.edu/cdm/ref/collection/ehsl-shw/id/351