Underlying structure of the National Institutes of Health Stroke Scale - Results of a factor analysis

Background and Purpose-No stroke scale has been validated as an outcome mea sure using data from a clinical trial demonstrating a positive therapeutic effect. Therefore, we proposed to use data from the National Institute of N eurological Disorders and Stroke (NINDS) tPA Stroke Trial to determine whet her the National Institutes of Health Stroke Scale (NIHSS) was valid in pat ients treated with tissue plasminogen activator (tPA) and to explore the un derlying clinimetric structure of the NIHSS. Methods-We performed an exploratory factor analysis of NIHSS data from Part 1 (n=291) of the NINDS tPA Stroke Trial to derive a hypothesized underlyin g factor structure. We then performed a confirmatory factor analysis of thi s structure using NIHSS data from Part 2 of the same trial (n=333). We then tested whether this final factor structure could be found in tPA- and plac ebo-treated patients serially over time after stroke treatment. Using 3-mon th outcome data, we tested for an association between the NIHSS and other m easures of stroke outcome. Results-The exploratory analysis suggested that there were 2 factors underl ying the NIHSS, representing left and right brain function, confirming the content validity of the scale. An alternative structure composed of 4 facto rs could be derived, with a better goodness of fit: the first 2 factors cou ld represent left brain cortical and motor function, respectively, and the second 2 factors could represent right brain cortical and motor function, r espectively. The same factor structures were then found in tPA and placebo patient groups studied serially over time, confirming the exploratory analy sis. All 3-month clinical outcomes were associated with each other at subse quent time points, confirming predictive validity. Conclusions-This is the first study of the validity of a stroke scale in pa tients treated with effective stroke therapy. The NIHSS appeared to be vali d in patients with acute stroke and for finding treatment-related differenc es. The scale was valid when used serially over time after stroke, up to 3 months, and showed good agreement with other measures of outcome.