Stroke Mimics: An Important Source of Bias in Acute Ischemic Stroke Research

Study Objective: Stroke mimics may be difficult distinguish from acute ischemic strokes and are often treated with alteplase though not by intent. We report the characteristics, frequency, and outcomes of stroke mimics treated at our institution. Using our data, we then explore how the inclusion of stroke mimics in stroke outcomes research may be an important source of bias. Methods: We retrospectively identified all patients treated with alteplase in our emergency department from August 2013 to December 2017 for suspected acute ischemic stroke. We collected the following variables: gender, age, risk factors (hypertension, diabetes, and atrial fibrillation), admission glucose, admission National Institute of Health Stroke Scale, admission mean arterial pressure, onset-to-treatment time, adverse events, discharge diagnosis, length of stay, discharge NIHSS, discharge destination, and 3 month modified Rankin score. Results: One hundred and eighteen patients were treated with alteplase for suspected acute ischemic stroke of which 33 (27.9%) were stroke mimics. Compared to ischemic strokes, stroke mimics were younger (median age 53 versus 69; P < .0003); were less likely to have vascular risk factors (hypertension 51.5% versus 78.8%; P < .005] diabetes (9.1% versus 32.9%; P < .007), and atrial fibrillation (3.0% versus 23.5%; P < .006). The most common stroke mimic was transient ischemic attack (33.3%). Stroke mimics were significantly more likely to be discharged home (75.8% versus 41.2%; P < .002). Outcomes unadjusted for stroke mimics led to artificial inflation of a favorable discharge destination. Conclusions: Inclusion of stroke mimics led to an artificial inflation of a favorable discharge destination for our entire cohort. Our study highlights the potential for bias in reporting favorable outcomes if appropriate adjustment accounting for stroke mimics does not occur.