What does the dissociation between the results of video head impulse versus caloric testingreveal about the vestibular dysfunction in Ménière’s disease?
McGarvie LA1, Curthoys IS, MacDougall HG, Halmagyi GM.
1Institute of Clinical Neurosciences, Royal Prince Alfred Hospital , Camperdown NSW , Australia.
It is suggested that the different results of rotational (video head impulse – vHIT) and caloric tests in patients with Ménière’s disease (MD) may be a consequence of the physical enlargement of the membranous duct in the hydropic labyrinths in MD, causing a reduced response to caloric stimulation.
There have been reports that the results of two tests of semicircular canal function, the caloric response and the responses to vHIT do not agree. This retrospective study at a tertiary referral hospital examined this disagreement.
This study reviewed the data of 22 patients who met the AAO-HNS criteria for MD and who had both caloric and vHIT testing.
There was a clear dissociation: patients with MD had a small or absent response to caloric stimulation of their affected ear, whilst their response to vHIT was in the normal range.
The accepted Gentine model of the mechanism of caloric stimulation could account for this dissociation: the increased diameter of the semicircular duct in hydropic labyrinths resulting in endolymph circulation within the duct itself and so a smaller thermally induced pressure across the cupula. The increased duct diameter will have little effect on responses to rotation.
VOR; head impulse test; nystagmus; semicircular canal; vHIT