Background: Postural stability in humans is largely maintained by vestibular, visual, and somatosensory
inputs to the central nervous system. Recent clinical advances in the assessment of
otolith function (e.g., cervical and ocular vestibular evoked myogenic potentials
[cVEMPs and oVEMPs], subjective visual vertical [SVV] during eccentric rotation) have
enabled investigators to identify patients with unilateral otolith impairments. This
research has suggested that patients with unilateral otolith impairments perform worse
than normal healthy controls on measures of postural stability. It is not yet known
if patients with unilateral impairments of the saccule and/or inferior vestibular
nerve (i.e., unilaterally abnormal cVEMP) perform differently on measures of postural
stability than patients with unilateral impairments of the horizontal SCC (semicircular
canal) and/or superior vestibular nerve (i.e., unilateral caloric weakness). Further,
it is not known what relationship exists, if any, between otolith system impairment
and self-report dizziness handicap.
Purpose: The purpose of this investigation was to determine the extent to which saccular impairments
(defined by a unilaterally absent cVEMP) and impairments of the horizontal semicircular
canal (as measured by the results of caloric testing) affect vestibulospinal function
as measured through the Sensory Organization Test (SOT) of the computerized dynamic
posturography (CDP). A secondary objective of this investigation was to measure the
effects, if any, that saccular impairment has on a modality-specific measure of health-related
quality of life.
Research Design: A retrospective cohort study. Subjects were assigned to one of four groups based
on results from balance function testing: Group 1 (abnormal cVEMP response only),
Group 2 (abnormal caloric response only), Group 3 (abnormal cVEMP and abnormal caloric
response), and Group 4 (normal control group).
Study Sample: Subjects were 92 adult patients: 62 were seen for balance function testing due to
complaints of dizziness, vertigo, or unsteadiness, and 30 served as controls.
Intervention: All subjects underwent videonystagmography or electronystagmography (VNG/ENG), vestibular
evoked myogenic potentials (VEMPs), self-report measures of self-perceived dizziness
disability/handicap (Dizziness Handicap Inventory), and tests of postural control
(Neurocom Equitest).
Data Collection and Analysis: Subjects were categorized into one of four groups based on balance function test
results. All variables were subjected to a multifactor analysis of variance (ANOVA). The Dizziness Handicap Inventory (DHI) total scores and equilibrium scores served
as the dependent variables.
Results: Results showed that patients with abnormal unilateral saccular or inferior vestibular
nerve function (i.e., abnormal cVEMP) demonstrated significantly impaired postural
control when compared to normal participants. However, this group demonstrated significantly
better postural stability when compared to the group with abnormal caloric responses
alone and the group with abnormal caloric responses and abnormal cVEMP results. Patients
with an abnormal cVEMP did not differ significantly on the DHI compared to the other
two impaired groups.
Conclusions: We interpret these findings as evidence that a significantly asymmetrical cVEMP in
isolation negatively impacts performance on measures of postural control compared
to normal subjects but not compared to patients with significant caloric weaknesses.
However, patients with a unilaterally abnormal cVEMP do not differ from patients with
significant caloric weaknesses in regard to self-perceived dizziness handicap.
Key Words
Dizziness handicap - postural stability - saccule - vestibular
