Reliability and Validity of the Canadian Neurological Scale in Retrospective Assessment of Initial Stroke Severity

BACKGROUND: Stroke severity is an important determinant of outcome, however, quantitative data on the initial neurological status might be lacking in retrospective studies. We wanted to assess the reliability and validity of the retrospective use of the Canadian Neurological Scale (CNS). METHODS: In 181 patients with validated stroke, two raters scored the CNS based on medical record review. We assessed interrater reliability and construct validity of the CNS. Predictive validity was assessed by the ability of the CNS to predict 30-day and 1-year mortality. RESULTS: Interrater reliability was high (kappa or weighted kappa 0.76-0.96). Correlations between similar items of prospective Scandinavian Stroke Scale scores and retrospective CNS scores ranged from 0.54 to 0.85. CNS total score was a strong predictor of death within 30 days and 1 year in multivariate models. CONCLUSIONS: The retrospective algorithm for the CNS had a high to substantial interrater reliability and predictive validity. Accordingly, in retrospective stroke studies using medical record information, the CNS can be a feasible instrument to adjust for differences in stroke severity.