Exploring slow-phase eye velocity and nystagmus duration following caloric irrigation in Ménière's disease

IntroductionIn the early years following the development of the caloric test, one of the parameters used to quantify vestibular function was nystagmus duration. A common finding in patients with Meniere's disease (MD) is the presence of unilateral caloric weakness, despite normal results on the video head impulse test (vHIT). It has been proposed that the apparent caloric loss could be due to the creation of local flow facilitated by canal distention. If the nystagmus duration is linked to the hydrostatic effect, one could hypothesize that MD patients would demonstrate shorter slow-phase velocity (SPV) duration.ObjectiveThe aim of the study was to examine SPV and the duration of nystagmus following caloric testing in MD patients.Method24 participants (12 controls; 12 MD) were assessed using bithermal, bilateral caloric stimulation. To control for possible side differences, two subgroups were analyzed: MD-ipsilateral (affected ear); MD-contralateral (unaffected ears). Ears in the control group were side matched with ears in the MD groups and the terminology control-ipsilateral or control-contralateral was used to represent this matching.ResultsSignificant differences were observed for SPV between controls-contralateral and MD-ipsilateral ears (cold: p ≤ 0.001; warm: p = 0.02) and between controls-ipsilateral and MD-ipsilateral ears (cold: p ≤ 0.001; warm: p = 0.04). Significant SPV differences were observed between MD-contralateral and MD-ipsilateral ears (cold: p ≤ 0.001; warm: p = 0.03). However, no differences were found between groups in the duration of nystagmus following cold or warm irrigation (cold: p = 0.2; warm: p = 0.33).ConclusionResults support previous literature suggesting SPV can be affected in patients with MD even if vHIT gain is normal. However, mechanisms that influence the SPV seem to differ from those for the nystagmus duration. Indeed, nystagmus duration seems to remain unaffected in MD patients with vHIT-caloric dissociation, suggesting that it may be controlled by other factors.