Otolith Function Assessed with the Subjective Postural Horizontal and Standardised Stance and Gait Tasks

Abstract

If otolith function is essential to maintain upright standing while moving along slanted or uneven surfaces, subjects with an otolith deficit should have difficulty judging whether the inclination of the surface on which they are standing is tilted or not. We tested this judgement and compared it with the ability to control trunk sway during standardised stance and gait tests. Thirteen patients with unilateral vestibular nerve neurectomy at least 6 months prior to testing and 39 age-matched controls were asked to move a dynamic posturography platform on which they were standing back to their subjective ‘horizontal’ position after the platform had been slowly tilted at 0.4°/s to 5° in 8 different directions. Normal subjects left the platform deviated in pitch (forwards-backwards) at about 0.7° on describing the platform as levelled off for all directions of tilt. Patients showed larger deviations of about 1.3° in pitch with significant differences for forward right tilt (1.58 ± 0.73° compared to 0.73 ± 0.11° for normals; mean and SEM) and for forward left. Roll (lateral) deviations were about 0.4° for normals and 0.5° larger for the patients (for example, for backward left, 1.13 ± 0.24° compared to 0.4 ± 0.07° in normals). Except for a tendency towards greater deviations to the lesion side of patients with eyes closed, no differences were noted between tests under eyes open and closed conditions. However, for backward and roll tilts patients needed to steady themselves first by grasping a handrail when tested with eyes closed. Stance tests on foam showed increases in roll and pitch trunk sway with respect to controls. Patients had significantly larger trunk roll sway deviations during 1-legged stance tests and during gait trials. For stance trials, the patients lost their balance control prior to the end of the standard 20-second recording time. We conclude that a unilateral loss of otolith inputs due to nerve resection permanently impairs the ability to judge whether the support surface is horizontal, and leads to excessive trunk sway when standing on a compliant surface as well as excessive trunk roll sway during gait.

Measurements of Trunk Sway for Stance and Gait Tasks 2 Years after Vestibular Neurectomy

“…Second, the neurectomy patients had complete otolith lesions. Similar results for stance and gait tasks were obtained by Beule and Allum [2006] for cerebellar pontine angle tumor patients after VN following tumor removal. Furthermore, Beule and Allum [2006] were also able to show that the ability to judge offsets from the true horizontal were impaired in their patient population, indicating a deficit in otolith responses.…”

“…In the event, we had very significant results for 14 subjects with low AAO-HNS scores. An alternative estimate of sample size would have been to take the number of patients used in a study of a similar population, those with a neurectomy due to removal of a cerebellar pontine angle tumor [Beule and Allum, 2006]. Beule and Allum [2006] showed similar results as our current study with 14 patients.…”

“…Tests of vestibulo-ocular reflex (VOR) function up to 3 years after vestibular schwannoma surgery show that gains for rotations to the deficit side are reduced to 50% of normal [Yamane et al, 1987;Beule and Allum, 2006]. These results are in line with results obtained with head impulse testing following neurectomies performed in case of intractable Ménière's disease [Aw et al, 1999].…”

Perception of the Postural Vertical and Falls in Older People

“…Beule and Allum [20] previously described a test of PPV whereby participants standing on a movable support platform were required to return the platform to the horizontal position following tilts in roll and pitch planes using a joystick. The authors found that patients with unilateral otolith disorders performed worse than healthy age-matched controls on this task, and suggested that this test could be used as a simple clinical test of otolith function.…”

“…Although recent research demonstrates the important role played by the somatosensory system to update humans’ internal models of verticality [18,19], in the absence of lower limb somatosensory and visual input, PPV is likely primarily modulated by the vestibular system [20]. In fact, Beule and Allum [20] reported that compared with healthy controls, patients with unilateral loss of otolith input showed significantly greater deviations from the vertical when asked to move the support platform on which they stood back to the vertical following forward left and right tilts as well as tilts in the roll plane. In addition, previous research has shown that while young healthy adults can report PPV accurately within a tight ‘angle of uncertainty’ [21], older people have greater difficulty re-aligning themselves vertically after being tilted [22,23].…”