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Persistent postural perceptual dizziness (PPPD) describes a persistent sensation of dizziness and/or unsteadiness (without vertigo) aggravated by upright posture that generates increased postural sway.1 Here, we introduce a novel measure of perceived instability to investigate the relationship between observed sway and perceived instability in patients with PPPD compared with patients with persistent ‘objective’ instability due to bilateral vestibulopathy (BV).
Overall, 19 individuals with PPPD, according to the diagnostic criteria of the International Classification of Vestibular Diseases and 10 disease controls with BV (confirmed with objective vestibular function testing), were included following informed consent. PPPD patients were randomly allocated to an ‘intervention’ (n=7) and ‘no intervention’ group (n=12). Ten healthy controls were also recruited to validate the novel measure of perceived instability.
Measurement of observed sway
All participants performed three identical 20 s trials of quiet standing on a firm surface with eyes closed, arms by the sides and feet together. Healthy controls stood on foam to increase instability.
Observed sway was measured using a force plate (EquiTest or Kistler 9281C1, Winterthur, Switzerland) and quantified as the centre of pressure mean velocity, calculated as total horizontal distance travelled over the trial divided by time (20 s).
Measurement of perceived instability
First, participants verbally rated their perceived instability during the observed sway measurements (‘how unstable did you feel during the trial?’) using a 0–10 ranked scale, where 0 corresponds to being ‘completely steady’ and 10 ‘so unsteady that I would fall’. Second, participants replicated their perceived instability by moving their body how they thought they were swaying during the observed sway measurements (‘move your body how you felt you were moving during the trial’). This perceived instability (herein termed ‘reproduced’ instability) was quantified by measuring sway while standing on the force plate with eyes open but otherwise in an identical manner to the observed instability …
ESPM and MJB contributed equally.
Contributors ESPM contributed to the conception and design of the study, acquisition and analysis of data and drafting of the manuscript. MJB contributed to the conception and design of the study, analysis of data and drafting of the manuscript and figures. PC contributed to acquisition and analysis of data and drafting of the manuscript. NK contributed to acquisition of data and drafting of the manuscript. DK conceived the study and contributed to the acquisition and analysis of data and drafting of the manuscript and figures, and approved the final version. All authors critically reviewed and approved of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.