Background: The National Institutes of Health Stroke Scale (NIHSS) was created to detect treatment-related differences in clinical trials and was designed to measure right- and left-sided cerebral hemispheric function.
Objective: To validate the original design in patients with very large strokes.
Design: A previously published factor structure was fit to the data. Then, a new analysis was conducted to explore the underlying structure of the scale in this population. Finally, NIHSS scores and infarction volumes were compared.
Setting: The Clomethiazole for Acute Stroke Study-Ischemic, conducted in academic and community hospitals.
Patients: Individuals with acute stroke seen within 12 hours of onset. Of 1191 records available, 98% had complete NIHSS scores.
Main outcome measure: Goodness-of-fit statistic (Bentler) for each factor solution.
Results: Two factors were found underlying the NIHSS, corresponding to the left and right hemispheres (goodness of fit = 0.97), using the previously published factor analysis. The new exploratory analysis also suggested 2 factors representing left and right brain function. The median (range) NIHSS scores were 15 (5-25) for right brain strokes and 19 (6-32) for left brain strokes (P<.001). The median (range) infarction volumes were 56.2 mL (0.1-381.5 mL) for right brain strokes and 37.8 mL (0.2-255.1 mL) for left brain strokes (P<.001). The correlation coefficient between NIHSS score and lesion volume was 0.37 (P<.001).
Conclusions: The underlying structure of the NIHSS conforms to cerebral hemispheric lateralization, confirming previous findings in a new population of large hemispheric strokes. Left- brain strokes score 4 points higher on the NIHSS than right brain strokes of larger volume.