Does the National Institutes of Health Stroke Scale favor left hemisphere strokes?

Background and Purpose-The National Institutes of Health Stroke Scale (NIHSS) is a valid, reproducible scale that measures neurological deficit. Of 42 possible points, 7 points are directly related to measurement of language compared with only 2 points related to neglect. Methods-We examined the placebo arm of the NINDS t-PA stroke trial to test the hypothesis that the total volume of cerebral infarction in patients with right hemisphere strokes would be greater than the volume of cerebral infarction in patients with left hemisphere strokes who have similar NIHSS scores. The volume of stroke was determined by computerized image analysis of CT films and CT images Stored on computer tape and optical disks. Cube-root transformation of lesion volume was performed for each CT, Transformed lesion volume was analyzed in a logistic regression model to predict volume of stroke by NIHSS score for each hemisphere. Spearman rank correlation was used to determine the relation between the NIHSS score and lesion volume. Results-The volume for right hemisphere stroke was statistically greater than the volume for left hemisphere strokes, adjusting for the baseline NIHSS (P<0.001). For each 5-point category of the NIHSS score <20, the median volume of right hemisphere strokes was approximately double the median volume of left hemisphere strokes. For example, for patients with a left hemisphere stroke and a 24-hour NIHSS score of 16 to 20, the median volume of cerebral infarction was 48 mt (interquartile range 14 to 111 mL) as compared with 133 mt (interquartile range 81 to 208 mLfor patients with a right hemisphere stroke (P<0.001). The median volume of a right hemisphere stroke was roughly equal to the median volume of a left hemisphere stroke in the next highest 5-point category of the NIHSS, The Spearman rank correlation between the 24-hour NIHSS score and 3-month lesion volume was 0.72 for patients with left hemisphere stroke and 0.71 for patients with right hemisphere stroke. Conclusions-For a given NIHSS score, the median volume of right hemisphere strokes is consistently larger than the median volume of left hemisphere strokes. The clinical implications of our finding need further exploration.