Introduction
Individuals with persistent postural-perceptual dizziness (PPPD) exhibit one or more of the following symptoms: unsteadiness, a sensation of floating, or non-rotating dizziness that is present almost every day for more than three months. “PPPD is precipitated by conditions that cause a balance disorder, including vestibular, psychiatric, and traumatic diseases, but the dizziness in PPPD cannot be explained by the conditions.” (Ichijo, et.al.) Dizziness can be made worse by standing stationary, with body movement, and with visual stimulation. In general, individuals feel worse when standing or walking compared to sitting or lying down.
A possible association between PPPD and reliance on visual cues has been suggested. The brain processes information received from the visual (eyes), vestibular (inner ear) and somatosensory (touch) systems to interpret posture and movement. Foam posturography is used to measure an individual’s sway (how he/she moves while trying to balance) in various conditions. Standing on a foam rubber mat decreases the ability to use somatosensory input from the feet. Closing the eyes disrupts the ability to use vision. Measuring sway during these conditions can evaluate whether individuals rely more on visual or somatosensory cues. The aim of this study was to assess postural sway of PPPD patients by comparing them to healthy controls.
Methods
PPPD patients included 12 men and 41 women, aged 18-84, recruited from the Balance Disorder Clinic at the University of Tokyo Hospital. Diagnosis was made based on criteria from the Barany Society. The subjects underwent testing to examine the function of the otolith organs (utricle, saccule) in the inner ear. The otolith organs help to sense linear motion and acceleration. Electromyographic (EMG) activity was recorded from a service electrode placed on the upper half of each sternocleidomastoid muscle in the neck (cervical VEMP) and from electrodes placed on the upper and lower eyelids (ocular VEMP).
The video head impulse test (vHIT) was also performed to examine the semicircular canals within the inner ear, which sense angular motion. This test used goggles, which recorded eye movements as the patient’s head was quickly moved side to side and up and down.
For the foam posturography test, experimenters used a force plate that subjects stood on with their feet together to measure velocity (speed) of sway and area of the movement. Subjects were tested under four conditions: Fixed/Open (eyes open standing on a hard surface), Fixed/Closed (eyes closed standing on a hard surface), Foam/Open (eyes open standing on foam mat), and Foam/Closed (eyes closed standing on foam mat). Each trial was timed for 60 seconds, or until the subject needed help to prevent them from falling.
The experimenters used observational study data to find 53 age- and sex-matched healthy subjects. Data from the 53 PPPD patients were compared with data from the 53 healthy subjects.
Results
In comparing posturography findings between healthy subjects and those with PPPD, the velocity (speed) of sway in the PPPD group was significantly higher than in the control group in the Fixed/Open Fixed/Closed, and Foam/Closed conditions. In the Foam/Open condition, the difference was not statistically significant. The area of sway in the PPPD group was significantly higher than that in the control group in the Fixed/Open, Fixed/Closed, Foam/Open, and Foam/Closed conditions.
In assessing Romberg’s ratios (the ratio of velocity or area with the eyes closed to that of the eyes open), the ratios were significantly higher in the PPPD group than in the control group in the Velocity/Fixed, Area/Fixed, Velocity/Foam, and Area/Foam conditions. These results suggest that the PPPD group was more dependent on visual input in a standing posture than the control group. The foam ratios were significantly higher in the control group than in the PPPD group in the Velocity/Open, Area/Open, Velocity/Closed, and Area/Closed conditions. These results suggest that the PPPD group tend to have less dependence on somatosensory cues in a standing posture than the control group.
Within the PPPD group, those that had abnormal VEMP and vHIT tests, falls occurred in all four conditions. In those with VEMP abnormal but vHIT normal, there were falls in all conditions except for the Fixed/Open condition. The VEMP normal and vHIT normal group had the smallest median value of velocity with Foam/Closed and Foam/Open conditions compared to others in the PPPD group.
Conclusion
The results of this study suggest that individuals with PPPD have higher postural instability and depend more on input from their vision while standing compared to healthy subjects. Also, PPPD patients tended to have lower dependence on somatosensory input in standing posture than healthy subjects. This information can be helpful in determining proper rehab protocols to help those recover from PPPD, especially in the physical therapy realm.
Summarized by: Danielle Beatty, DPT
Acknowledgements: Thanks to the Journal of Vestibular Research for granting VeDA access to this article.