New Developments in Attentional Rehabilitation
Abstract & Commentary
By Marc Dinkin, MD, Assistant Professor of Ophthalmology, Weill Cornell Medical College. Dr. Dinkin reports no financial interest in this field of study
Synopsis: The presence of conjugate eye deviation as measured by CT or MRI in acute stroke patients predicts visuo-spatial neglect. Prismatic therapy produces a cross-modality improvement in left-sided auditory extinction in patients with chronic right-sided stroke.
Sources: Becker E, et al. Neuroimaging of eye position reveals spatial neglect. Brain 2010:133:909-914; Jacquin-Courtois S, et al. Effect of prism adaptation on left dichotic listening deficit in neglect patients: Glasses to hear better? Brain 2010:133;895-908.
Spatial neglect is a relatively common finding in patients who have suffered a right-hemisphere acute stroke and has the potential to severely affect daily functioning and quality of life. Visuo-spatial neglect may be measured using clinical tests such as letter cancellation, but such tasks are time consuming and may not feasible in patients who are too debilitated to participate. It has been found that the presence of ipsilesional conjugate eye deviation (CED) correlates with the size of hemispheric lesions involving the right middle and superior temporal gyri. Electro-oculography has shown CED in patients with left-sided spatial neglect, but this technique is not easily available in the inpatient setting. CT scans, which are already acquired in acute stroke, offer an alternative method of measuring CED, and were utilized by Simon et al to predict lesion side.
Becker and colleagues used CT or MRI images at presentation to investigate whether CED could distinguish patients with hemispheric strokes and spatial neglect from those that did not have neglect. Among 71 patients, the average degree of ipsilesional CED was significantly higher in those with spatial neglect (~10°) than those who simply had hemispheric lesions, (< 5°). Lesion size was used as a covariate factor, ameliorating the confounding effect that CED might be more likely to occur with larger lesions, which in turn might be associated with neglect. Finally, the inclusion of the right superior and middle temporal gyri in the lesion area correlated better with the degree of CED than any other location, although the effect was not significant.
One rehabilitative strategy for patients with left visuo-spatial neglect due to right hemispheric lesion involves the use of bilateral prisms, which shift the visual world to the right by 10°. The patient is then asked to point at a series of 50 targets located in both sides of the midline. Over the session, this therapy leads to a recalibration of the visuo-proprioceptive map and has been shown to improve visual hemispatial neglect. Jacquin-Courtois and colleagues investigated whether or not this prismatic adaptation could also lead to improvement in left-sided auditory neglect in patients with chronic right hemispheric strokes. Dichotic auditory stimuli (two words heard simultaneously in right and left earphones) were presented to patients with left-sided auditory neglect, and a laterality index was generated representing the asymmetry of correctly identified words. Surprisingly, one session of prismatic shift therapy led to a significant amelioration in left auditory extinction at both 0 and 2 hours post-therapy, while sham therapy with non-prismatic goggles did not.
Becker's study has powerful clinical implications, as it suggests that brain imaging, which is already performed in every stroke patient, can be used to predict the presence of spatial neglect without any need for patient cooperation or additional clinical testing. This finding could lead to earlier recognition and even quantification of spatial neglect, although they have not yet shown that the degree of deviation correlates well with the degree of neglect. Although the association between CED and neglect has already been shown in EOG studies, the demonstration of this principle using neuro-imaging adds to the credibility of this more practical methodology.
The authors did not address the presence of visual field defects in 20% of the patients with right hemispheric lesions and spatial neglect. Could such a field defect contribute to ipsilesional CED as patients searched the available visual landscape? This is unlikely, since patients without spatial neglect were more likely to have a field defect in this study, and still showed less CED. Nevertheless, the conclusions would have been strengthened by including visual field defect as a covariate in their analysis and by the use of more sensitive formal visual field analysis.
Jacquin-Courtois's results support the notion that adaptation of neglect in response to prismatic therapy is modulating higher order determinants of spatial orientation that are not specific to visual or proprioceptive modalities. When patients learn to recalibrate visual to proprioceptive stimuli during the therapy, this change appears to apply to auditory mapping as well. The effects of auditory neglect are increasingly recognized, and may be particularly troublesome for patients with low vision who may use auditory clues to navigate and for social interactions. The clinical importance of this study, therefore, lies not only in what it says about the neuro-anatomical basis of prismatic adaptation, but in that it offers a feasible and efficacious therapy to these patients.
With earlier recognition and quantification of visual neglect using neuro-imaging and the use of a novel means of treating auditory neglect with the established therapy of prismatic shift, these studies together may lead to real improvements in the post-stroke care of patients with spatial neglect.