Progressive vestibular impairment in patients with polyneuropathy.

It is generally assumed that imbalance in patients with polyneuropathy (PNP) results from deficient proprioceptive input arriving from the lower limbs. Polyneuropathic processes, however, may also impair vestibular function. In fact, we observed that two-thirds of patients with PNP show unilateral or bilateral impairment of vestibular function as assessed with search-coil head impulse testing. In the present work, we analyzed the same database of 37 polyneuropathic patients to find out whether the presence of a unilateral or bilateral vestibular deficit reflects a progression of the vestibular impairment. Results suggest that vestibular function in PNP patients deteriorates asymmetrically, first affecting one side and later both sides.

Deficient high-acceleration vestibular function in patients with polyneuropathy.

BACKGROUND: Unsteadiness during standing and walking is a frequent complaint of patients with polyneuropathy (PNP). OBJECTIVE: To determine whether balance disorders in patients with PNP may be caused by reduced proprioceptive input from the feet alone or whether impaired vestibular input, resulting from involvement of the vestibular nerve, can be an additional factor. METHODS: A total of 37 patients (mean age 65 years +/- 12 SD; 12 women) with electrodiagnostically confirmed PNP (predominantly axonal: 18; predominantly demyelinating: 19) underwent horizontal search-coil head-impulse testing, which assesses the high-acceleration vestibulo-ocular reflex (VOR). RESULTS: Relative to a healthy comparison group, the gains (eye velocity divided by head velocity) of the horizontal VOR were reduced in 27 of 37 patients (unilateral: 13; bilateral: 14). The percentages of patients with unilateral or bilateral VOR deficits were not significantly different between patients with axonal or demyelinating PNP. CONCLUSIONS: Two thirds of patients with axonal or demyelinating polyneuropathy (PNP) showed unilateral (approximately 50%) or bilateral (approximately 50%) gain reductions of the horizontal high-acceleration vestibulo-ocular reflex. This finding suggests that, in many patients with PNP, the neuropathic process includes the vestibular nerve. Such information is highly relevant for subsequent physical therapy, since vestibular exercise improves balance control and reduces disability.

Torsional vestibulo-ocular reflex during whole-body oscillation in the upright and the supine position: II. Responses in patients after vestibular neuritis.

In a recent study we demonstrated that otolith input modifies the torsional angular vestibulo-ocular reflex (torVOR) of healthy human subjects: Compared to turntable oscillations in supine position, oscillations in upright position increased the gain of torVOR by 0.1 and cancelled the phase lead originating from low-frequency semicircular canal signals. We asked whether these otolith-related changes of torVOR are still present in patients after vestibular neuritis (VN). Eight patients were sinusoidally oscillated about their naso-occipital axis in supine (canal-only stimulation) and upright (canal-and-otolith stimulation) position. Three-dimensional eye movements were recorded with dual search coils. The patients showed similar otolith-related gain and phase changes of the torVOR as healthy subjects: the gain increased by about 0.1 (p < 0.05) and the low-frequency phase lead from semicircular canal signals was abolished. These results indicate that otolith function after VN is still sufficient to interact with semicircular canal signals to optimize torsional gaze stabilization when the head is upright.

Caloric and search-coil head-impulse testing in patients after vestibular neuritis.

The objective of this study was to compare results of quantitative head-impulse testing using search coils with eye-movement responses to caloric irrigation in patients with unilateral vestibular hypofunction after vestibular neuritis. The study population consisted of an acute group (<3 days; N = 10; 5 male, 5 female; 26-89 years old) and a chronic group (>2 months; N = 14; 8 male, 6 female; 26-78 years old) of patients with unilateral vestibular hypofunction after vestibular neuritis. The testing battery included: (1) simultaneous measurement of eye and head rotations with search coils in a magnetic coil frame during passive Halmagyi-Curthoys head-impulse testing and (2) electronystagmography during bilateral monaural 44 degrees C-warm and 30 degrees C-cold caloric irrigation. The main outcome measures were (1) the gain of the horizontal vestibulo-ocular reflex during search-coil head-impulse testing and (2) the amount of canal paresis during caloric irrigation. All acute and chronic patients had a unilateral gain reduction during search-coil head-impulse testing. A pathological canal paresis factor was present in 100% of the acute patients but in only 64% of the chronic patients. The clinically suspected unilateral vestibular hypofunction resulting from vestibular neuritis was validated in all acute patients by both search-coil head-impulse and caloric testing. Hence, either of these tests is sufficient for diagnosis in the acute phase of vestibular neuritis. Chronic patients, however, were reliably identified only by search-coil head-impulse testing, which suggests that the low-frequency function of the labyrinths often becomes symmetrical, leading to a normal canal paresis factor.

Vertical divergence and counterroll eye movements evoked by whole-body position steps about the roll axis of the head in humans.

In healthy human subjects, a head tilt about its roll axis evokes a dynamic counterroll that is mediated by both semicircular canal and otolith stimulation, and a static counterroll that is mediated by otolith stimulation only. The vertical ocular divergence associated with the static counterroll too is otolith-mediated. A previous study has shown that, in humans, there is also a vertical divergence during dynamic head roll, but this report was not conclusive on whether this response was mediated by the semicircular canals only or whether the otoliths made a significant contribution. To clarify this issue, we applied torsional whole-body position steps (amplitude 10 degrees, peak acceleration of 90 degrees /s(2), duration 650 ms) about the earth-vertical (supine body position) and earth-horizontal (upright body position) axis to healthy human subjects who were monocularly fixating a straight-ahead target. Eye movements were recorded binocularly with dual search coils in three dimensions. The dynamic parameters were determined 120 ms after the beginning of the turntable movement, i.e., before the first fast phase of nystagmus. The static parameters were measured 4 s after the beginning of the turntable movement. The dynamic gain of the counterroll was larger in upright (average gain: 0.48 +/- 0.10 SD) than in supine (0.36 +/- 0.10) position. The static gain of the counterroll in the upright position (0.21 +/- 0.06) was smaller than the dynamic gain. Divergent eye movements (intorting eye hypertropic) evoked during the dynamic phase were not significantly different between supine (average vergence velocity: 0.87 +/- 0.51 degrees /s) and upright (0.84 +/- 0.64 degrees /s) positions. The static vertical divergence in upright position was 0.32 +/- 0.14 degrees. The results indicate that the dynamic vertical divergence in contrast to the dynamic ocular counterroll is not enhanced by otolith input. These results can be explained through the different patterns of connectivity between semicircular canals and utricles to the eye muscles. Alternatively, we hypothesize that the small dynamic vertical divergence represents the remaining vertical error necessary to drive an adaptive control mechanism that normally maintains a vertical eye alignment.

Torsional vestibulo-ocular reflex during whole-body oscillation in the upright and the supine position. I. Responses in healthy human subjects.

In rhesus monkeys, the dynamic properties of the torsional vestibulo-ocular reflex (VOR) are modified by otolith input: compared with torsional oscillations about an earth-vertical axis (canal-only stimulation), the phase lead observed at frequencies below 0.1 Hz is cancelled when the animals are rotated about an earth-horizontal axis (canal-and-otolith stimulation); the gains of the torsional VOR, however, are nearly identical in both conditions. To test whether or not canal-otolith interaction in humans is similar to that in rhesus monkeys, we examined ten healthy human subjects on a three-axis servo-controlled motor-driven turntable. The subjects were oscillated in upright or supine position in complete darkness over a similarly wide range of frequencies (0.05-1.0 Hz) with peak velocities <40 degrees/s. Eye movements were recorded using the three-dimensional search coil technique. Compared with the torsional vestibulo-ocular gains during canal-stimulation only (earth-vertical axis), the gains obtained during combined canal-otolith-stimulation (earth-horizontal axis) were significantly higher throughout the entire frequency range (P<0.05). The gain increased by 0.100+/-0.074 (SD), independent of frequency. During the earth-horizontal axis stimulation, the phase remained always around zero, which is in contrast to the canal-stimulation only, during which one finds an increasing phase lead as frequency decreases. We conclude that, in healthy humans as in rhesus monkeys, the phase lead from the canal signals at low frequencies is effectively cancelled by the otolith input. In contrast to rhesus monkeys, however, otolith signals in healthy humans increase the gain of the torsional VOR at frequencies from 0.05 to 1.0 Hz. This normal database is crucial for the interpretation of results obtained in patients with vestibular disorders.

[Infrared and video oculography--alternatives to electrooculography?]. / Die Infrarot- und die Videookulographie--Alternativen zur Elektrookulographie?

With the introduction of each new technique for registering eye movements, the question arises concerning whether these provide a reliable and accurate alternative for the diagnosis of labyrinthine dysfunction when compared to the most commonly used electro-oculographic technique. To answer this question we compared mean slow-phase velocity (SPV) using three different recording techniques:electro-oculography (EOG), video-oculography (VOG) and infrared oculography (IROG) during four different types of examinations. The examinations were the eye target tracking test (ETT), horizontal and vertical optokinetic nystagmus (OKN) tests and the rotating chair test of the horizontal vestibulo-ocular reflex (HVOR). For the ETT tests the VOG provided consistently higher mean SPV values with low variance, presumably because of the accuracy and stability of the calibration. For the horizontal OKN and VOR rotating chair tests no significant differences were found between the mean SPV obtained with the different recording techniques, although the IROG recordings were associated with a larger variance. Vertical OKN mean SPV was consistently lower with IROG and VOG techniques presumably because of non-linearities and resolution limitations inherent in these techniques. These results indicate that the EOG technique despite its disadvantages of noise, time to apply and variability of calibration still provides an inexpensive, reliable and accurate means of measuring slow-phase eye movements.

Vestibulo-ocular responses during static head roll and three-dimensional head impulses after vestibular neuritis.

This study aimed to investigate whether unilateral vestibular neuritis (VN) causes the same deficits of ocular counter-roll during static head roll (OCR(S)) and dynamic vestibulo-ocular reflex gains during head impulses (VOR(HI)) as unilateral vestibular deafferentation (VD). Ten patients with acute and 14 patients with chronic vestibular paralysis after VN were examined. The testing battery included fundus photography of both eyes with the head upright (binocular cyclorotation) and dual search coil recordings in a three-field magnetic frame. With one dual search coil on the right eye and the other on the forehead, the following stimuli were given: i) Halmagyi-Curthoys head impulses about the vertical, horizontal and torsional axes. ii) Static roll positions of the head up to 20 degrees right- and left-ear-down by movement of the neck. The comparison group consisted of 19 healthy subjects. Compared with the VD-patients, as reported in the literature, acute VN-patients showed the same pattern of OCR(S) gain reduction and binocular cyclorotation (CRb). The main feature that distinguished chronic VN-patients from chronic VD-patients was the normalization of the torsional VOR(HI) gain to the affected side, whereas the VOR(HI) gains in the horizontal and vertical directions did not show recovery (as in the patients with chronic VD). Chronic VN-patients differed from acute VN-patients by: i) symmetrical OCR(S) gains, ii) a less pronounced CRb toward the affected side, and iii) a normal torsional VOR(HI) gain toward the affected side. Since the ipsilesional torsional VOR(HI) gain did not recover in VD-patients, the normalization of this gain in our VN-patients can only be explained by a (partial) recovery of otolith function on the side of the lesion after the neuritis.