The interpretation of video head-impulse tests (video-HITs) can often be complicated, limiting their clinical utility in acute vestibular syndrome. We aimed to determine video-HIT findings in patients with posterior circulation strokes (PCS) and vestibular neuritis (VN). We retrospectively analyzed the results of video-HITs in 59 patients with PCS. Irrespective of the actual lesion revealed later on MRIs, ipsilateral and contralateral sides were assigned according to the direction of slow-phase of spontaneous nystagmus (SN). Then, the patterns of video-HIT findings were classified according to the vestibulo-ocular reflex (VOR) gain for the horizontal canals; 1) ipsilaterally positive, 2) contralaterally positive, 3) bilaterally normal, and 4) bilaterally positive. The abnormal responses were further defined into 5) wrong-way saccades, 6) perverted, and 7) early acceleration followed by premature deceleration. We also analyzed the asymmetry of the corrective saccadic amplitude between the sides, calculated from the sum of cumulative saccadic amplitudes on both sides. The results were compared with video-HIT results from 71 patients with VN. Video-HITs were normal in 32 (54%), ipsilaterally positive in 11 (19%), bilaterally positive in 10 (17%), and contralaterally positive in six (10%) patients with PCS. Wrong-way saccades were more frequently observed in VN than PCS [31/71 (44%) vs. 5/59 (9%), p < 0.001]. Saccadic amplitude asymmetry was greater in VN than PCS [median = 100% (IQR = 82-144, 95% CI = 109-160) vs. 0% (-29-34, -10-22, p < 0.001)]. When differentiating VN from PCS, the sensitivity was 81.7%, and specificity was 91.5% at the cut-off value of 71% for saccadic amplitude asymmetry with an area under the curve (AUC) of 0.91 (95% CI = 0.86-0.97). The AUC for saccadic amplitude asymmetry was larger than that for the ipsilateral VOR gain (p = 0.041) and other parameters. Patients with PCS may show various head-impulse responses that deviate from the findings expected in VN, which include normal, contralaterally positive, and negative saccadic amplitude asymmetry (i.e. a greater cumulative saccadic amplitude contralaterally). A thorough analysis of corrective saccades in video-HITs can improve the differentiation of PCS from VN even before MRIs.

Objective To determine the mechanism of ictal downbeat nystagmus in Ménière disease (MD), we compared the head impulse gain of the vestibulo-ocular reflex (VOR) for each semicircular canal between patients with (n = 7) and without (n = 70) downbeat nystagmus during attacks of MD. Methods We retrospectively analyzed the results of video-oculography, video head-impulse tests, and cervical vestibular-evoked myogenic potentials (VEMPs) in 77 patients with definite MD who were evaluated during an attack. Results Pure or predominant downbeat nystagmus was observed in 7 patients (9%) with unilateral MD during the attacks. All 7 patients showed spontaneous downbeat nystagmus without visual fixation with a slow phase velocity ranging from 1.5 to 11.2°/s (median 5.4, interquartile range 3.7–8.5). All showed a transient decrease of the head impulse VOR gains for the posterior canals (PCs) in both ears (n = 4) or in the affected ear (n = 3). Cervical VEMPs were decreased in the affected (n = 2) or both ears (n = 2) when evaluated during the attacks. Downbeat nystagmus disappeared along with normalization of the VOR gains for PCs after the attacks in all patients. During the attacks, the head impulse VOR gains for the PC on the affected side were lower in the patients with ictal downbeat nystagmus than in those without (Mann-Whitney U test, p < 0.001), while the gains for other semicircular canals did not differ between the groups. Conclusion Downbeat nystagmus may be observed during attacks of MD due to an asymmetry in the vertical VOR or saccular dysfunction. MD should be considered in recurrent audiovestibulopathy and ictal downbeat nystagmus.

Introduction: Carbon monoxide (CO) poisoning can result in delayed neurological sequelae (DNS). Factors predicting DNS are still controversial. This study aims to determine whether acute brain lesions observed using diffusion-weighted magnetic resonance imaging (MRI) following acute CO poisoning are related to the subsequent development of DNS. Methods: This prospective study was conducted on patients with CO poisoning treated at a university hospital in Bucheon, Korea. From August 2016 to July 2019, a total of 283 patients visited the hospital because of CO poisoning. Exclusion criteria included age under 18 years, refusing hyperbaric oxygen therapy, refusing MRI, being discharged against medical advice, being lost to follow-up, having persistent neurological symptoms at discharge, and being transferred from another hospital 24 h after exposure. Results: Of the 154 patients included in the final study, acute brain lesions on MRI (ABLM) were observed in 49 patients (31.8%) and DNS occurred in 30 patients (19.5%). In a logistic regression analysis, lower Glasgow coma scale score and higher exposure time were associated with DNS, and the presence of ABLM in white matter was significantly associated with DNS (OR 6.741; 95% CI, 1.843–24.660; p = 0.004). Conclusion: The presence of ABLM in white matter was significantly related to the occurrence of DNS. Early prediction of the risk of developing DNS through MRI may be helpful in treating patients with CO poisoning.