Using vestibular evoked myogenic potentials to localise brainstem lesions. A preliminary report

Vestibular Evoked Myogenic Potentials (VEMPs) are saccular responses to acoustic stimuli. They can be recorded from the sternocleidomastoid muscle ipsilaterally to the stimulated ear. Their reflex arc includes the ipsilateral vestibular nuclei. To determine the usefulness of VEMPs in localising brainstem lesions. We used VEMPs, Blink Reflex (BR) and Brainstem Auditory Evoked Responses (BAERs) to evaluate six patients presenting with acute ischaemic or haemorrhagic brainstem lesions, or basilar dolichoectasia. MRI in patient one revealed a dorsolateral medullary infarct on the right. VEMP amplitude was reduced ipsilaterally. The R2 BR component was delayed bilaterally upon stimulation of the affected side. Patients two and three had suffered a left lateral lower pontine infarct and a right lateral lower pontine haemorrhage. In patients four and five, MRA revealed dolichoectasia of the basilar artery exerting pressure on the lower lateral pons. VEMP amplitude was reduced ipsilaterally. Patient six had an ischaemic lesion in the right upper lateral pons. The R1, R2i and R2c BR components were delayed ipsilaterally. BAERs waves IV and V were absent on the right. VEMPs were normal. VEMPs are affected by lesions of the lateral lower pons and upper medulla. Our results suggest that they may be a useful addition in the localisation of such lesions.