Interconversion of the National Institutes of Health Stroke Scale and Scandinavian Stroke Scale in Acute Stroke

Introduction

The National Institutes of Health Stroke Scale (NIHSS) and Scandinavian Stroke Scale (SSS) are both validated measures of neurologic impairment and have been used in many acute stroke trials. Methods for interconverting SSS and NIHSS are needed.

Methods

Conversion equations were developed using linear regression (both unadjusted, and adjusted for age and sex) using a random 50% of the data at both baseline and 90 days. The remaining 50% of data were used to test the accuracy of the models produced.

Results

Data from 5 acute stroke trials (2004 patients) were included. Fitted models at baseline were NIHSS = 25.68 – 0.43 ∗ SSS (R² = 0.57, prediction error [PE] –0.2, P = .20), and SSS = 50.37 – 1.63 ∗ NIHSS (R² = 0.59, PE 0.2, P = .35). The 90-day models were NIHSS = 22.99 – 0.39 ∗ SSS (R² = 0.82, PE –0.3, P = .001), and SSS = 56.68 – 2.20 ∗ NIHSS (R² = 0.80, PE –0.4, P = .08). Adjustment did not materially improve the R² values.

Conclusion

Total scores for NIHSS and SSS may be interconverted with good precision; the mathematic conversion equations may prove useful in clinical practice and in comparison of data from observational studies and randomized trials.

Key Words: Stroke, severity, clinical trial