44 - Cryptogenic Stroke

Abstract

In a percentage of patients, a defined etiology of ischemic stroke is not identified. These patients are categorized as cryptogenic (unknown cause) ischemic stroke. The estimated percentage of ischemic strokes that are cryptogenic varies from 15% to 35%, reflecting the lack of a standardized definition for cryptogenic ischemic stroke, inconsistency of the extent and quality of etiologic diagnostic testing, variable types of populations included (e.g., younger vs. older), and differences in the attribution of causality to some common findings. The percentage of patients categorized as cryptogenic ischemic stroke also varies by etiologic classification scheme. Cryptogenic ischemic stroke may comprise three groups: under-classified, under-measured, and truly cryptogenic strokes. “Under-classified” represents populations where an etiology is present (e.g., carotid disease), but does not fulfill strict criteria for diagnosis (<50%). “Under-measured” represents a population where diagnostic evaluation is incomplete, especially in those with a high probability of large-vessel disease or atrial fibrillation. True cryptogenic ischemic stroke is defined by a thorough but normal diagnostic evaluation. The natural history of recurrent major vascular events in patients with cryptogenic ischemic stroke is strongly associated with population characteristics. In older populations, the risk of recurrent stroke is high, while in younger populations with truly cryptogenic stroke, the risk of recurrent stroke is low. Most cryptogenic ischemic strokes have an embolic topology and may be better described as “embolic stroke of undetermined source.” The rationale for this classification is to define a minimum set of diagnostic tests and identify a patient population for clinical trials.