Background. Subjective unsteadiness or dizziness, usually without increase in body
sway, is common in older people. The absence of mechanistic understanding of such
symptoms renders clinical management difficult. Here, we explore the mechanisms behind
such idiopathic dizziness, focusing on postural control abnormalities.
Methods. Thirty patients with idiopathic dizziness and 30 age-matched controls stood
on a moving platform. Platform oscillations were randomly delivered at different velocities
(from 0 to 0.2m/s). Markers of postural control, including objective sway (trunk sway path,
recorded via a sensor attached to vertebrae C7), stepping responses, subjective instability and
anxiety ratings were obtained. MRI scans were available for correlations with levels of
cerebral small vessel disease in 28 patients and 24 age-matched controls.
Results. We observed a significant relationship between objective and subjective
instability in all groups. The slope of this fit was significantly steeper for patients than controls,
indicating greater perceived instability for the same body sway. Stepwise linear regression
showed the slopes of this objective-subjective instability relationship were best explained by
concerns about falling (Falls Efficacy Scale-International), clinical physical functioning (Short
Physical Performance Battery) and, to some degree, by neuroimaging markers of cerebral
small vessel disease. In addition, patients had a reduced stepping threshold, suggesting an
overly-cautious postural response.
Conclusion. The distorted perception of instability and subtle impairments in balance
control, including abnormal and overly-cautious stepping responses, underlies the emergence
of idiopathic dizziness. It appears to relate to changes in postural performance, psychological
functioning, and disruption of postural brain networks associated with cerebral small vessel disease.