Dorsolateral medullary infarction: a neurogenic cause of a contralateral, large-amplitude vestibular evoked myogenic potential.

The vestibular evoked myogenic potential (VEMP) has become a useful tool to assess the saccule and inferior vestibular nerve function. Vestibulopathies involving the saccule or inferior vestibular nerve typically result in VEMP responses that are diminished or absent on the involved side. Abnormally large VEMPs are rare. Large VEMPs have been associated with superior canal dehiscence, Ménière's disease, and labyrinthine fistula. In all of these cases, the abnormally large VEMP can be explained on the basis of labyrinthine hydromechanical changes that result in excessive saccular displacement in response to intense sound. In this report, a case is presented of a 74-year-old male with dorsal lateral medullary infarction (Wallenberg's syndrome) who presented with an enlarged VEMP--a finding that has not been reported to date as a result of a brain stem lesion. Particularly perplexing, the enlarged VEMP was on the contralesional side. A proposed mechanism of contralateral vestibular nuclei disinhibition secondary to the brain stem stroke is discussed.