Post headshake nystagmus: further correlation with other vestibular test results.

BACKGROUND: It is generally accepted that headshake nystagmus (HSN) is generated from an asymmetrical peripheral vestibular input and a correlation exists between HSN and canal paresis. There have been limited reports, however, how HSN correlates with the more recently introduced tests of vestibular function. AIMS/OBJECTIVES: To evaluate the correlation between HSN and unilateral weakness on caloric testing, high-frequency vestibulo-ocular reflex (VOR) function on video head impulse testing (VHIT) and otolith function determined by vestibular evoked myogenic potentials (VEMPs). METHODS: A retrospective study of all patients who underwent complete vestibular function testing at our tertiary referral center from 2016 to 2019 was performed. Demographic data, clinical diagnosis (where available), the results of video-nystagmography, vHIT, and VEMPs were evaluated. RESULTS: Of the 1499 patients in the study period, 101 (6.7%) had HSN. Vestibular test abnormalities were more common in patients with HSN. The sensitivity of HSN for underlying pathology was low in comparison with vestibular testing. However, HSN demonstrated a high specificity. CONCLUSIONS AND SIGNIFICANCE: HSN generation is likely more complex than caloric-induced nystagmus, probably due to additional variables within the vestibular system. HSN may provide clinicians with additional information concerning high-frequency VOR function involving lateral semicircular and otolith dysfunction.

Videonystagmography and Posturography.

Videonystagmography (VNG) and posturography are two vestibular assessment techniques that are still in use today. VNG: VNG allows clinicians to observe and record eye movements in real-time. Compared with electronystagmography (ENG), VNG tracings are more detailed and can capture subtle clinical findings. The utility of the monothermal caloric screen has been proposed in various studies. When appropriate cut-offs are used, the monothermal screen can be completed with a low false-negative rate. Air is often used as a medium for caloric testing, though not without some controversy. When air and water are compared, the response magnitudes for air are consistently smaller than for water. However, the overall classification of the result appears to be generally the same regardless of the caloric medium used. Posturography: Concerns have been raised about the reliability and validity of posturographic measurements. Approaches and analysis techniques vary widely, and there is little consensus regarding the best approaches for assessment or interpretation. There is a need for standardized protocols. The portable and low-cost Nintendo Wii Balance Board (WBB) has inspired a surge in publications looking at the validity of the system for quantifying posturography and for balance training; preliminary findings are very promising.

Vestibular stimulation improves insight into illness in schizophrenia spectrum disorders.

Impaired insight into illness (IMP-INS) is common among individuals with schizophrenia spectrum disorders (SSD), contributing to medication nonadherence and poor clinical outcomes. Caloric vestibular simulation (CVS) is typically used to assess peripheral vestibular system function. Left cold CVS is also a transiently effective treatment for IMP-INS and hemineglect secondary to right brain hemisphere stroke, and possibly for IMP-INS and mood stabilization in patients with SSD. Participants with SSD and moderate-to-severe IMP-INS participated in an exploratory double blind, crossover, randomized controlled study of the effects of CVS on IMP-INS. Participants sequentially received all experimental conditions-left cold (4°C), right cold, and body temperature/sham CVS-in a random order. Repeated measures ANOVA were performed to compare changes in IMP-INS, mood and positive symptom severity pre and 30min post CVS. A significant interaction was found between CVS condition, time, and body temperature nystagmus peak slow phase velocity (PSPV) for IMP-INS, indicating that single session left cold CVS transiently improved IMP-INS while right cold CVS may have worsened IMP-INS, particularly in participants with greater vestibular reactivity (i.e. higher PSPV) to body temperature CVS. The procedure's effectiveness is attributed to stimulation of underactive right hemisphere circuits via vestibular nuclei projections to the contralateral hemisphere.