Prognosis of Cryptogenic Ischemic Stroke: A Prospective Single-Center Study in Chile

Approximately 25%-40% of ischemic strokes are considered of unknown cause (ie, cryptogenic). The available information on associated risk factors, functional outcome, and recurrence of this subtype of stroke is limited, especially for the Chilean population. We conducted a prospective cohort study of 380 patients aged ≥18 years admitted consecutively to a stroke unit with demonstrated ischemic stroke. The stroke subtypes were classified according to the Trial of Org 10172 in Acute Stroke Treatment criteria. The modified Rankin Scale score and Barthel Index were used to assess functional outcome. The Kaplan‒Meier product-limit method and Cox proportional hazards regression analysis were used to identify predictors of recurrent stroke during the follow-up period (mean, 2.1 years). Cryptogenic stroke (CS) was diagnosed in 76 patients (20%), 55.2% of them male, with a mean age of 62 ± 17 years. CS was the third most common stroke subtype after the large-artery disease (29%) and cardioembolic (24.4%) subtypes. After adjustment for age and sex, no vascular risk factors or laboratory parameters assessed at the time of admission were found to be predictive of CS. The CS subtype had the lowest rate of stroke recurrence at the end of the follow-up period (n = 4; 2.5% per year; odds ratio, 0.32; 95% confidence interval, 0.11-0.91; P = .022), a favorable functional outcome (mean modified Rankin Scale score, 2; mean Barthel Index, 77), and no increase in mortality risk (odds ratio, 0.73; 95% confidence interval, 0.29-1.77; P = .48). Our findings demonstrate that patients with no definite etiology identified after an extensive workup are at lower risk of recurrence and more likely to have a favorable outcome. No risk factors distinguish CS from other stroke subtypes in our study population.