The National Institute of Health Stroke Scale (NIHSS) is biased toward dominant hemisphere infarcts, demonstrating greater functional deficits. This lateralization of the NIHSS deficit has been shown to adversely affect stroke recognition and outcome. Therefore, understanding factors that modify the association between infarct laterality and NIHSS severity is important. Age has been shown to be a factor in lateralization of brain function but it’s unclear if age affects lateralization of the NIHSS deficit. Leukoaraiosis commonly presents in the elderly and can be used as a marker for age. In this study, the authors hypothesized that leukoaraiosis modifies the association between infarct laterality and NIHSS severity.
Authors retrospectively analyzed consecutive patients with acute supratentorial ischemic strokes over a one year span. Baseline characteristics, including NIHSS, and modified rankin scale (mRS) at 90 days were recorded. Leukoaraiosis was defined as white matter hypoattenuation on FLAIR sequences and graded according to the Fazekas scale within periventricular and subcortical regions. Degree of leukoaraiosis was dichotomized to non-to-mild (score of 0-2) and severe (score of 3-6).
In total, 238 patients were included for analysis. Patients with left hemispheric infarcts had significantly greater NIHSS scores than right hemispheric infarcts. Hemispheric lateralization of NIHSS was only present in patients with non-to-mild leukoaraiosis. Severe leukoaraiosis attenuated the hemispheric lateralization of NIHSS. In multivariable linear regression models, leukoaraiosis, not chronological age, predicted NIHSS-deficit severity.
This study found that severe leukoaraiosis is associated with a remarkable attenuation of NIHSS-bias. The leukoaraiotic brain, due to loss of white matter tract, relies on recruitment of additional functional domains thereby becoming more susceptible for functional deficits after an ischemic stroke irrespective of laterality. This study serves as a reminder to not exclude patients for thrombolytics and endovascular therapy based solely on a low NIHSS as this scale is biased toward usually left hemispheric infarcts. This study provides insight into how leukoaraiosis affects cerebral functioning.
