Vestibular Dysfunction Linked With Abnormal Balance in Parkinson Disease

Imbalance in patients with Parkinson disease (PD) was found to be significantly associated with decreased vestibular processing, according to study findings published in the Journal of Neurological Sciences.

Defined as the integration of both peripheral vestibular labyrinth and central vestibular system functions, the vestibular system has been implicated, albeit in conflicting findings, in the pathophysiology of parkinsonian imbalance—one of the most challenging symptoms of PD that is poorly responsive to dopaminergic therapy.

Researchers note that a major limitation in research investigating the association between vestibular dysfunction and imbalance in patients with PD is the lack of adjustment for confounder effects of visual or somatosensory postural processing functions, cognition, or the severity of striatal dopaminergic losses.

“The major objective of this study was to examine the association between vestibular measures of dynamic posturography and abnormal balance in PD while controlling for confounder variables,” they said.

“We previously have shown that decreases in striatal dopamine associated with normal aging do not impair the ability of the vestibular control system indicating that this likely represents a nondopaminergic function.”

A total of 106 enrolled patients with PD were included in the cross-sectional study. Participants underwent the Sensory Organization Test (SOT) using the Neurocom Equitest device while on their usual dopaminergic medications, which consisted of 6 sensory testing conditions assessing the integration of proprioceptive, visual, and vestibular functions during upright standing.

All SOT measures, nigrostriatal dopaminergic denervation, brain acetylcholinesterase, age, duration of disease, cognitive and parkinsonian motor scores, and ankle vibration sensitivity were used as regressors in a stepwise logistic regression model comparing patients with PD vs normal controls (n = 29).

“Total center of pressure (COP) excursion and COP RMS were calculated to estimate postural sway. Postural steadiness COP functions were defined as time domain measures of distance, area (RMS), velocity, and frequency-domain measures of spectral magnitude or distribution. Therefore, the following 3 COP measures were selected as primary outcome variables: COP RMS, COP velocity, and COP frequency,” explained the study authors.

Among the study cohort, the average [SD] Montreal Cognitive Assessment (MOCA) test score was 26 (2.3) (range 19-30), average [SD] duration of motor symptoms observed among PD patients was 6.1 [4.1] years (range, 0.5-19), average [SD] Hoehn and Yahr (HY) stage among patients was 2.4 [0.6] (range, 1-4.0), and mean [SD] Movement Disorder Society-revised Unified Parkinson's disease Rating Scale (UPDRS) in the medication “off” state after withholding of dopaminergic medication overnight was 37.1 [14.7] (range, 9.5-73.5).

Abnormal balance was present in 73 out of 106 patients with PD, defined as HY stage 2.5 or higher.

Findings showed that the presence of imbalance was significantly associated with vestibular ratio COP RMS (P = .002) independently from visual ratio COP velocity (P = .012), thalamic acetylcholinesterase activity (P = .0032), cognition (P = .006), motor severity (P = .0039), age (P = .001), ankle vibration sensitivity (P = .0008), and borderline findings for somatosensory ratio COP velocity (P = .074) and visual ratio COP RMS (P = .078). No significant association was observed between presence of imbalance and nigrostriatal dopaminergic denervation.

Limitations of the analysis included the lack of vestibular testing based on nystagmography or caloric testing to identify a vestibular peripheral or central deficit more precisely in patients with PD.

“Further research is needed to investigate an intrinsic role of the cholinergic thalamus in multi-sensory, in particular vestibular, processing functions of postural control in PD,” concluded the study authors.

Reference

Bohnen NI, Roytman S, Griggs A, David SM, Beaulieu ML, Müller MLTM. Decreased vestibular efficacy contributes to abnormal balance in Parkinson's disease. J Neurol Sci. 2022 Sep 15;440:120357. doi:10.1016/j.jns.2022.120357