Background and purpose: The National Institutes of Health Stroke Scale (NIHSS) is an established measure of neurological impairment; however, it can award more points for tests of presumed left-hemisphere function, such as language, than for tests of right-hemisphere function, such as neglect. This difference may be important if a low NIHSS score is used to exclude patients with right-hemisphere stroke from clinical trials or established treatments. The aim of this study was to investigate whether the relationship between acute NIHSS score and acute stroke volume as determined by acute diffusion- and perfusion-weighted MRI (DWI and PWI) differs between right- and left-sided stroke.
Methods: This was a retrospective study of 153 patients with acute stroke seen at Beth Israel Deaconess Medical Center between January 1995 and March 2000 who underwent an MRI examination and NIHSS within 24 hours of stroke onset. NIHSS score was recorded prospectively by the admitting stroke fellow at the time of acute presentation, immediately preceding imaging. Computerized volumetric analysis of the MRI lesions was performed by investigators blinded to clinical data.
Results: There were significant correlations between the acute NIHSS scores and acute DWI lesion volumes (r=0.48 right, r=0.58 left) and between acute NIHSS scores and perfusion-weight imaging hypoperfusion volumes (r=0.62 right, r=0.60 left). For patients with NIHSS scores of 0 to 5, the DWI volume of right cerebral lesions was greater than that of left-sided lesions (mean volume, 8.8 versus 3.2 cm3; P=0.04). Among patients with DWI lesions larger than the median volume (9 cm3), 8 of 37 with right-sided stroke had an NIHSS score of 0 to 5 compared with 1 of 39 patients with left-sided stroke (P=0.01). Multiple linear regression analysis revealed a significantly lower acute NIHSS on the right compared with the left side when adjusted for stroke volume on chronic T2 imaging (P=0.03).
Conclusions: Patients with right-sided stroke may have a low NIHSS score despite substantial DWI lesion volume. Acute imaging information, such as that available with multimodal MRI, may be useful to identify patients for inclusion in acute stroke protocols when there is clinical uncertainty about eligibility. Prospective evaluation of criteria incorporating acute imaging data is required.