Aspects of cerebral plasticity related to clinical features in acute vestibular neuritis: a "starting point" review from neuroimaging studies

A Review of Neuroimaging Studies in Persistent Postural-Perceptual Dizziness (PPPD)

Persistent postural-perceptual dizziness (PPPD) is a functional vestibular disease characterized by persistent dizziness, unsteadiness, and/or non-spinning vertigo, and is the most common vestibular syndrome in young adults. A stiffened postural control strategy, shift to reliance on visual over vestibular information, and hypervigilance to the environment have been suggested as possible pathophysiological mechanisms of PPPD. However, the exact mechanisms remain unclear. Recently, neuroimaging studies using magnetic resonance imaging and single photon emission computed tomography have provided pivotal insights into the pathophysiology of PPPD. The aim of this review was to evaluate and summarize the existing data on neuroimaging studies in PPPD. In summary, these studies fairly consistently reported decreased brain structure, function, and connectivity among the areas involved in multisensory vestibular processing and spatial cognition, and increased function and connectivity in the visual processing areas in patients with PPPD. The detected brain changes might reflect maladaptive and compensatory mechanisms including dysfunctional integration of multisensory vestibular information and visual dependence. Notably, various factors including personality traits (i.e., neuroticism), psychiatric comorbidities (i.e., anxiety and depression), and triggering factors (i.e., peripheral vestibular lesions) seem to modulate brain functional activity and connectivity patterns, possibly accounting for some differences across the results. Future studies should carefully control for these confounding effects in order to draw firm conclusions.

Binocular cyclotorsion in superior vestibular neuritis

SUMMARY

Conjugated cyclotorsion of the eyes toward the affected side can commonly be observed in vestibular neuritis. The aim of this study was to assess the differences in cyclotorsion between the ipsi- and contralesional eye during selective involvement of the superior branch of the vestibular nerve. We studied binocular cyclotorsion through ocular fundus photographs in 10 patients affected by acute superior vestibular neuritis (SVN). Cyclotorsion was also studied in 20 normal subjects. All SVN patients showed an ipsilesional cycloversion of the eyes. Normal subjects exhibited a constant mild excyclovergence (6.42 ± 2.34°). In SVN patients, contralateral incyclotorsion (8.4 ± 8.14°) was lower and not normally distributed compared to ipsilateral eye excyclotorsion (17.9 ± 4.36°) with no correlation between them. The interocular difference in cyclodeviation could be related to the starting physiological excyclovergence, to different tonic effects on the extraocular muscles of the two eyes and to the different influence of spontaneous nystagmus on cyclodeviation in the two eyes. We recommend referring only to ipsilateral excyclotorsion in the evaluation of utricular function during SVN and its subsequent compensation. Further studies are required to determine the binocular cyclotorsion in the case of other kinds of selective involvement of the vestibular nerve.