Characteristics and outcomes of unknown onset stroke: The Japan Stroke Data Bank

Background: Clinical outcomes of unknown onset stroke (UOS) are influenced by the enlargement of the therapeutic time window for reperfusion therapy. This study aimed to investigate and describe the characteristics and clinical outcomes of patients with UOS. Methods: Patients with acute ischemic stroke (AIS) who were admitted within 24 h of their last known well time, from January 2017 to December 2020, were included. Data were obtained from a long-lasting nationwide hospital-based multicenter prospective registry: the Japan Stroke Data Bank. The co-primary outcomes were the National Institutes of Stroke Scale (NIHSS) scores on admission and unfavorable outcomes at discharge, corresponding to modified Rankin Scale (mRS) scores of 3–6. Results: Overall, 26,976 patients with AIS were investigated. Patients with UOS (N = 5783, 78 ± 12 years of age) were older than patients with known onset stroke (KOS) (N = 21,193, 75 ± 13 years of age). Age, female sex, higher premorbid mRS scores, atrial fibrillation, and congestive heart failure were associated with UOS in multivariate analysis. UOS was associated with higher NIHSS scores (median = 8 [interquartile range [IQR]: 3–19] vs. 4 [1–10], adjusted incidence rate ratio = 1.37 [95% CI: 1.35–1.38]) and unfavorable outcomes (52.1 vs. 33.6%, adjusted odds ratio = 1.27 [1.14–1.40]). Intergroup differences in unfavorable outcomes were attenuated among females (1.12 [0.95–1.32] vs. males 1.38 [1.21–1.56], P = 0.040) and in the subgroup that received reperfusion therapy (1.10 [0.92–1.33] vs. those who did not receive therapy 1.23 [1.08–1.39], P = 0.012). Conclusions: UOS was associated with unfavorable outcomes but to a lesser degree among females and patients receiving reperfusion therapy.