Development of a Conversion Factor to Facilitate Comparison of National Institute of Health Stroke Scale Scores with Scandinavian Stroke Scale Scores

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Abstract
The National Institute of Health Stroke Scale (NIHSS) and the Scandinavian Stroke Scale (SSS) are commonly used in clinical stroke trials. Use of different scales in trials makes comparison of outcomes difficult. Adult patients with an acute stroke were recruited within 24 h of onset, and NIHSS, SSS and Glasgow Coma Scale scores were assessed at baseline and repeated at 1 week. A total of 144 patients were included (46% males, mean age = 73 years). At presentation the median SSS score was 38 (2-58), and a week later 40 (4-58), the median NIHSS score at presentation was 5 (0-29) and a week later 3 (0-27). Changes in both scales were strongly correlated, r = 0.76, p < 0.001. Both were good predictors of mortality. Linear regression analysis produced an equation relating the two: SSS = 50 - 2 x NIHSS.