Gaze instability after exposure to moving visual stimuli in patients with persistent postural-perceptual dizziness

Is Vestibular Rehabilitation as Effective for Persistent Postural-Perceptual Dizziness as for Chronic Unilateral Vestibular Hypofunction?

OBJECTIVE

To compare the feasibility and outcomes of vestibular rehabilitation (VR) for persistent postural-perceptual dizziness (PPPD) with those for chronic unilateral vestibular hypofunction (UVH).

STUDY DESIGN

Prospective study.

SETTING

Tertiary referral center.

PATIENTS

Nineteen consecutive patients with chronic UVH lasting for >3 months and 15 with PPPD.

INTERVENTIONS

The VR program consisted of gaze stabilization exercises, static or dynamic balance exercises and gait training, and habituation exercises that exposed patients to a provocative stimulus. Patients were asked to perform VR for at least 20 min a day.

MAIN OUTCOME MEASURES

Status of VR (i.e., continuation/discontinuation) and outcomes were assessed 1 month after the introduction of VR using the Dizziness Handicap Inventory for handicaps in daily life due to dizziness, the Niigata PPPD Questionnaire (NPQ) for symptom exacerbations of PPPD, and the Hospital Anxiety and Depression Scale for anxiety and depression.

RESULTS

No patients in the chronic UVH group discontinued VR, whereas six patients in the PPPD group discontinued VR owing to symptom exacerbations, showing a significant difference. VR did not decrease any symptom scale, except for the NPQ-motion subscore, in patients with PPPD who continued VR, whereas it decreased all clinical symptom scales, except for the NPQ-motion subscore, in patients with chronic UVH.

CONCLUSIONS

Patients with PPPD had a higher rate of VR discontinuation than those with chronic UVH, and VR was less effective in patients with PPPD who even continued treatment than in those with chronic UVH. Therefore, VR on PPPD should be optimized.

Research Progress on the Potential Pathogenesis of Persistent Postural-Perceptual Dizziness

INTRODUCTION

Persistent postural-perceptual dizziness (PPPD) is the most prevalent chronic functional dizziness in the clinic. Unsteadiness, dizziness, or non-spinning vertigo are the main symptoms of PPPD, and they are typically aggravated by upright posture, active or passive movement, and visual stimulation. The pathogenesis of PPPD remains incompletely understood, and it cannot be attributed to any specific anatomical defect within the vestibular system. Consequently, there is no objective examination method for the disease, and the diagnosis primarily depends on the symptoms of the patient, which lack specificity.

METHODS

To better understand the pathogenesis of PPPD and to aid in the development of novel diagnostic strategies and therapies, we conducted a comprehensive narrative review of the relevant literature. We performed a search for literature in PubMed using the following search phrases: "persistent postural-perceptual dizziness" OR "PPPD" OR "chronic subjective dizziness" OR "functional dizziness" OR "space-motion discomfort" OR "visual vertigo" OR "phobic postural vertigo." The reference list of relevant studies was also screened. The search was limited to publications in English, and the final references were selected based on their relevance to the scope of this review.

RESULTS

This review summarizes recent studies that have investigated the pathogenesis of PPPD. It is traditionally assumed that PPPD may result from altered postural control strategies, cortical integration of threat assessment and spatial orientation, or abnormal integration of multi-sensory information. Recent studies have shown that the brain structure, activity, structural connectivity, and even cerebral perfusion of patients with PPPD differ from those of healthy individuals. Furthermore, PPPD patients are different from healthy individuals in spatial navigation ability, vestibular perception thresholds, central sensitization, and oxidative stress. These findings provide additional anatomical and behavioral insights into the pathogenesis of PPPD, suggesting that PPPD may arise from shifts in the interactions among emotional, visuo-vestibular, and sensorimotor networks.

CONCLUSION

Understanding the complex pathogenesis of PPPD is crucial for the development of novel therapeutics against PPPD. Following the existing findings, our review suggests directions for future research.

Persistent postural-perceptual dizziness: A functional neuro-otologic disorder

Persistent postural-perceptual dizziness (PPPD) is a functional neuro-otologic disorder that is the most frequent cause of chronic vestibular syndrome. The core vestibular symptoms include dizziness, unsteadiness, and non-spinning vertigo, which are exacerbated by an upright posture or walking, active or passive motion, and exposure to moving or complex visual stimuli. PPPD is mostly precipitated by acute or episodic vestibular diseases; however, its symptoms cannot be accounted for by its precipitants. PPPD is not a diagnosis of exclusion, but may coexist with other structural diseases. Thus, when diagnosing PPPD, the patient's symptoms must be explained by PPPD alone or by PPPD in combination with a structural illness. PPPD is most frequently observed at approximately 50 years of age, with a female predominance. Conventional vestibular tests do not reveal any specific signs of PPPD. However, the head roll-tilt subjective visual vertical test and gaze stability test after exposure to moving visual stimuli may detect the characteristic features of PPPD, that is, somatosensory- and visually-dependent spatial orientation, respectively. Therefore, these tests could be used as diagnostic tools for PPPD. Regarding the pathophysiology of PPPD, neuroimaging studies suggest shifts in interactions among visuo-vestibular, sensorimotor, and emotional networks, where visual inputs dominate over vestibular inputs. Postural control also shifts, leading to the stiffening of the lower body. To treat PPPD, selective serotonin reuptake inhibitors/serotonin noradrenaline reuptake inhibitors, vestibular rehabilitation, and cognitive behavioral therapy are used alone or in combination.

Functional Dizziness as a Spatial Cognitive Dysfunction

(1) Background: Persistent postural-perceptual dizziness (PPPD) is a common chronic dizziness disorder with an unclear pathophysiology. It is hypothesized that PPPD may involve disrupted spatial cognition processes as a core feature. (2) Methods: A cohort of 19 PPPD patients underwent psycho-cognitive testing, including assessments for anxiety, depression, memory, attention, planning, and executive functions, with an emphasis on spatial navigation via a virtual Morris water maze. These patients were compared with 12 healthy controls and 20 individuals with other vestibular disorders but without PPPD. Vestibular function was evaluated using video head impulse testing and vestibular evoked myogenic potentials, while brain magnetic resonance imaging was used to exclude confounding pathology. (3) Results: PPPD patients demonstrated unique impairments in allocentric spatial navigation (as evidenced by the virtual Morris water maze) and in other high-demand visuospatial cognitive tasks that involve executive functions and planning, such as the Towers of London and Trail Making B tests. A factor analysis highlighted spatial navigation and advanced visuospatial functions as being central to PPPD, with a strong correlation to symptom severity. (4) Conclusions: PPPD may broadly impair higher cognitive functions, especially in spatial cognition. We discuss a disruption in the creation of enriched cognitive spatial maps as a possible pathophysiology for PPPD.