Background--Early recovery after intravenous thrombolysis can be observed in stroke; however, the utility of measuring clinical improvement to assess artery status has not been established. We sought to determine the accuracy of serial National Institutes of Health Stroke Scale (NIHSS) scores to detect complete early recanalization of the middle cerebral artery.

Methods and Results--Data from the CLOTBUST trial (Combined Lysis of Thrombus in Brain Ischemia Using Transcranial Ultrasound and Systemic tPA) were used to determine the most sensitive and specific NIHSS-derived parameter to identify complete recanalization. Then, reproducibility was tested against a separate patient population (Barcelona data set). NIHSS scores were determined before tissue plasminogen activator bolus and at 60 and 120 minutes in both data sets. Receiver operating characteristic curves were used to compare test performance. The accuracy of individual cutoffs was demonstrated by sensitivity, specificity, and positive and negative predictive values. A total of 122 patients in the CLOTBUST data set and 98 in the Barcelona data set received 0.9 mg/kg intravenous tissue plasminogen activator [mean age 69±12 versus 72±12 years, 57% male versus 51% male, median NIHSS 16 versus 17 points, mean time from onset to treatment 140±32 versus 177±59 minutes, and complete recanalization of the middle cerebral artery in 19% versus 17%). For identification of recanalization, an NIHSS score reduction of 40% offered the best tradeoff, with sensitivity, specificity, positive predictive value, and negative predictive value of 65%, 85%, 50%, and 91% at 60 minutes and 74%, 80%, 58%, and 89% at 120 minutes, respectively. Test performance was equal in the Barcelona data set.

Conclusions--Relative changes in serial NIHSS scores can serve as a simple clinical indicator of arterial status after intravenous thrombolysis. Accuracy parameters are affected by the process of recanalization and its varying clinical significance.