Validation of minor stroke definitions for thrombolysis decision making

Background: Patients with low National Institutes of Health Stroke Scale (NIHSS) scores are frequently excluded from thrombolysis, but more than 25% of them remain disabled. We sought to define a validated minor stroke definition to reduce the inappropriate treatment exclusion. Methods: From an outcome database, untreated patients with an NIHSS score of 5 or less presenting within a 4.5-hour window were identified and 3-month modified Rankin Scale (mRS) outcomes were analyzed according to individual isolated symptoms and total NIHSS scores. The validity of the following minor stroke definitions were assessed: (1) the National Institute of Neurological Disorders and Stroke Tissue Plasminogen Activator (NINDS-TPA) trials' definition, (2) the total NIHSS score, varying a cutoff point from 0 to 4, and (3) our proposed definition that included an NIHSS score = 0 or an NIHSS score = 1 on the items of level of consciousness (LOC), gaze, facial palsy, sensory, or dysarthria. Results: Of 647 patients, 172 patients (26.6%) had a 3-month unfavorable outcome (mRS score 2-6). Favorable outcome was achieved in more than 80% of patients with an NIHSS score of 1 or less or with an isolated symptom on the LOC, gaze, facial palsy, sensory, or dysarthria item. In contrast, unfavorable outcome proportion was more than 25% in patients with an NIHSS score of 2 or more. When the NINDS-TPA trials' definition, our definition, or the definition of an NIHSS score of 1 or less were applied, more than 75% of patients with an unfavorable outcome were defined as a non-minor stroke and less than 15% of patients with an unfavorable outcome were defined as a minor stroke. Conclusion: Implementation of an optimal definition of minor stroke into thrombolysis decision-making process would decrease the unfavorable outcomes in patients with low NIHSS scores.