Acute Ischemic Stroke of Undetermined Etiology in a University Hospital
Objectives: Ischemic stroke is classified as of undetermined etiology in approximately 30% of cohorts in many clinical studies of stroke, including the Trial of ORG 10172 in Acute Stroke Treatment (TOAST). We investigated this undetermined etiology classification in our own in-hospital ischemic stroke population, and sought to determine clinical features of acute ischemic stroke which may be more or less predictive of an undetermined etiology. Methods: The medical records of patients admitted to the University Hospital with ischemic stroke between 1990 and 1998 were reviewed. Etiologic classification was determined based on imaging and other studies according to the TOAST criteria as atherothrombotic, embolic, lacunar, of other determined etiology, and of undetermined etiology (UND). The last category was then subdivided into negative evaluation (UND-1), more than one cause identified (UND-2), and incomplete evaluation (UND-3). Clinical features that might predict undetermined etiology were assessed, including severity, age, gender, and previously known ischemic stroke risk factors. Results: Of 690 patients with ischemic stroke, 163 (23.6%) had undetermined etiology. Men and women had a similar rate of UND. In the categories UND-1, UND-2, and UND-3 there were 39 (5.7%), 52 (7.5%), and 72 (10.4%) patients respectively. Stroke with severe paresis and diminished sensorium had a low frequency of undetermined etiology (13%, p < 0.01), with the majority of the UND as UND-3. A determination of UND was made in 34% of patients under 50 (p < 0.01), and in 32% of patients without known ischemic stroke risk factors (p < 0.05). These 2 patient groups combined were 24.3% of the cohort and more than 55% of their UND diagnoses were UND-1. Patients with lacunar syndrome had a high rate of UND-2 (10.8%, p < 0.05), and patients over age 75 had a low rate of UND-1 (1.4%, p < 0.01). Conclusions: In clinical studies of ischemic stroke a determination of undetermined etiology may be due to an incomplete evaluation, or more than one likely cause, rather than a negative evaluation. There are clinical features on presentation of ischemic stroke that are predictive of a classification of undetermined etiology.