Threshold for NIH Stroke Scale in Predicting Vessel Occlusion and Functional Outcome after Stroke Thrombolysis

BACKGROUND: Data are limited on optimal threshold for baseline National Institutes of Health Stroke Scale in predicting outcome after stroke thrombolysis (intravenous thrombolysis). AIMS: Finding thresholds for baseline National Institutes of Health Stroke Scale scores that predict functional outcome and baseline vessel occlusion. METHODS: We analyzed 44 331 patients with available modified Rankin Scale score at three-months and 11 632 patients with computed tomography/magnetic resonance angiography documented vessel occlusion at baseline in the SITS-International Stroke Thrombolysis Register. Main outcomes were functional independency (modified Rankin Scale 0-2) at three-months and baseline vessel occlusion. We obtained area under the curves by receiver operating characteristic analysis and calculated multivariately adjusted odds ratio for the outcomes of interest based on baseline National Institutes of Health Stroke Scale scores. RESULTS: For functional independency, National Institutes of Health Stroke Scale scores of 12 (area under the curve 0·775) and for baseline vessel occlusion, scores of 11 (area under the curve 0·678) were optimal threshold values. For functional independency, adjusted odds ratio decreased to 0·07 (95% CI 0·05-0·11), and for presence of baseline occlusion, aOR increased to 3·28 (95% CI 3·04-3·58) for National Institutes of Health Stroke Scale scores 12 and 11, respectively, compared with National Institutes of Health Stroke Scale score 0. National Institutes of Health Stroke Scale thresholds decreased with time from stroke onset to imaging, with 2-3 points, respectively, if time to imaging exceeded three-hours. CONCLUSIONS: Ideally, all acute stroke patients should have immediate access to multimodal imaging. In reality these services are limited. Baseline National Institutes of Health Stroke Scale scores of 11 and 12 were identified as markers of baseline vessel occlusion and functional independency after intravenous thrombolysis, respectively. These values are time dependent; therefore, a threshold of National Institutes of Health Stroke Scale 9 or 10 points may be considered in the prehospital selection of patients for immediate transfer to centers with multimodal imaging and availability of highly specialized treatments.