Abstract
Vestibular rehabilitation of patients in whom the level of vestibular function is continuously changing requires different strategies than in those where vestibular function rapidly becomes stable: where it recovers or where it does not and compensation is by catch-up saccades. In order to determine which of these situations apply to a particular patient, it is necessary to monitor the vestibulo-ocular reflex (VOR) gains, rather than just make a single measurement at a given time. The video Head Impulse Test (vHIT) is a simple and practical way to monitor precisely the time course and final level of VOR recovery and is useful when a patient has ongoing vestibular symptoms, such as after acute vestibular neuritis. In this study, we try to show the value of ongoing monitoring of vestibular function in a patient recovering from vestibular neuritis. Acute vestibular neuritis can impair function of any single semicircular canal (SCC). The level of impairment of each SCC, initially anywhere between 0 and 100%, can be accurately measured by the vHIT. In superior vestibular neuritis the anterior and lateral SCCs are the most affected. Unlike after surgical unilateral vestibular deafferentation, SCC function as measured by the VOR can recover spontaneously after acute vestibular neuritis. Here we report monitoring the VOR from all 6 SCCs for 500 days after the second attack in a patient with bilateral sequential vestibular neuritis. Spontaneous recovery of the VOR in response to anterior and lateral SCC impulses showed an exponential recovery with a time to reach stable levels being longer than previously considered or reported. VOR gain in response to low-velocity lateral SCC impulses recovered with a time constant of around 100 days and reached a stable level at about 200 days. However, in response to high-velocity lateral SCC and anterior SCC impulses, VOR gain recovered with a time constant of about 150 days and only reached a stable level toward the end of the 500 days monitoring period.
Highlights
In humans and in animals, total surgical deafferentation of one labyrinth immediately produces a permanent, severe deficit of the angular vestibulo-ocular reflex (VOR) responses to rapid angular head accelerations in the off-direction of any semicircular canal (SCC) on the intact side
All vertical bins used were for head velocities in the range 120–150◦/s. (Figures 1A,B, 2): The calculated VOR gains for Test 2 were: Right SCCs
The results obtained from this technique were a time constant of 150 days (R2 of fit = 0.99) for the high velocity right lateral SCC impulses, a time constant of 98 days (R2 of fit = 0.997) for the low velocity right lateral SCC impulses and a time constant of 164 days (R2 of fit = 0.977) for the right anterior SCC impulses
Summary
In humans and in animals, total surgical deafferentation of one labyrinth immediately produces a permanent, severe deficit of the angular vestibulo-ocular reflex (VOR) responses to rapid angular head accelerations in the off-direction of any semicircular canal (SCC) on the intact side. Catch-up, compensatory saccades substitute for the eye position error created by the VOR deficit; their cumulative magnitude is an index of the total VOR deficit during a head impulse. These are the fundamental principles underlying the video Head Impulse Test (vHIT) [1]. We report the results of meticulous monitoring of the VOR over 500 days, with vHIT from each of the 6 SCCs of a single patient with acute vestibular neuritis and show that spontaneous recovery of SCC function can take longer than generally expected with consequences for the patient’s recovery and rehabilitation. Our aim is to emphasize the ease and value of regular vHIT monitoring of the VOR during recovery from a peripheral vestibular lesion
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