Retrospective assessment of initial stroke severity with the Canadian Neurological Scale

Background and Purpose The severity of the initial neurological deficit is a critical determinant of outcome after acute stroke. Retrospective outcome studies are generally limited by a lack of quantitative data relating to this initial stroke severity. We evaluated the validity and reliability of measuring initial stroke severity retrospectively with the Canadian Neurological Scale (CNS). Methods The CNS was used to prospectively score the initial neurological deficit in a series of patients with acute ischemic stroke (n=24). An algorithm was devised for applying the CNS retrospectively on the basis of information in the patient's hospital discharge summary. Those dictating the discharge summaries were not aware of the study, and the retrospective scoring was performed without reference to other scores. The level of agree ment between the prospective and retrospective scores (validity) and both intraobserver and interobserver reliability for the retrospective scores were determined. Results Agreement was high between retrospective and prospective scores (r=.84, R-2=.71, P<.0001), between two sets of retrospective scores obtained by one rater (r=.95, R-2=.91, P<.0001), and between retrospective scores obtained by different raters (r=.91, R-2=.82, P<.0001). Weighted kappa statistics (kappa(W)) for prospectively versus retrospectively scored items varied from almost perfect (kappa(W)>0.81 for level of consciousness and orientation) to substantial (kappa(W)=0.68 for speech) and moderate (kappa(W)=0.41 to 0.60 for facial weakness, proximal arm, distal arm, proximal leg, and distal leg strength). Using the retrospective algorithm, there was almost perfect intraobserver and interobserver reliability for each of the individual CNS items (kappa(W)=0.81 to 1.00). Conclusions These data show that retrospective scoring of initial stroke severity using an algorithm based on the CNS is valid and can be reliably performed using information available in hospital discharge summaries.