Background Very few comparative studies have focused on the differences in the causes of ischemic stroke between young adults and non-young adults. This study was performed to determine what causes of ischemic stroke are more important in young adults than in non-young adults using a large-scale multicenter hospital-based stroke registry in Fukuoka, Japan. Methods and results We investigated data on 15,860 consecutive patients aged ≥18 years with acute ischemic stroke (mean age: 73.5 ± 12.4 years, 58.2% men) who were hospitalized between 2007 and 2019. In total, 779 patients were categorized as young adults (≤50 years of age). Although vascular risk factors, including hypertension, diabetes mellitus, and dyslipidemia, were less frequent in young adults than in non-young adults, the prevalence of diabetes mellitus and dyslipidemia in young adults aged >40 years were comparable to those of non-young adults. Lifestyle-related risk factors such as smoking, drinking, and obesity were more frequent in young adults than in non-young adults. As young adults became older, the proportions of cardioembolism and stroke of other determined etiologies decreased, but those of large-artery atherosclerosis and small-vessel occlusion increased. Some embolic sources (high-risk sources: arterial myxoma, dilated cardiomyopathy, and intracardiac thrombus; medium-risk sources: atrial septal defect, nonbacterial thrombotic endocarditis, patent foramen ovale, and left ventricular hypokinesis) and uncommon causes (vascular diseases: reversible cerebral vasoconstriction syndrome, moyamoya disease, other vascular causes, arterial dissection, and cerebral venous thrombosis; hematologic diseases: antiphospholipid syndrome and protein S deficiency) were more prevalent in young adults than in non-young adults, and these trends decreased with age. Conclusions Certain embolic sources and uncommon causes may be etiologically important causes of ischemic stroke in young adults. However, the contribution of conventional vascular risk factors and lifestyle-related risk factors is not negligible with advancing age, even in young adults.
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