Etiologic classification of ischemic stroke: Where do we stand?

•Currently available approaches to ischemic stroke classification are either causative or phenotypic.•The TOAST classification is the most widely used system for establishing ischemic stroke etiology.•Modified TOAST classifications with improved reliability have been developed but their wide use is still limited.•Development of an ideal etiological classification of ischemic stroke is impeded by the lack of a gold standard.

Despite major technological advances in ischemic stroke diagnostic techniques, our current understanding of stroke mechanisms and etiology continues to remain unclear in a significant percent of patients. As a result, several etiological ischemic stroke classifications have emerged during the last two decades but their reliability and validity is far from perfect and further world-wide research is needed in order to achieve the so much needed “standard reference language”. An ideal ischemic stroke classification should both comprise all underlying pathologies that could potentially concur to an index event and emphasize the most likely etiological and pathophysiological mechanism. Currently available approaches to ischemic stroke classification are either phenotypic or causative in nature, a multitude of criteria being published by different authors. Phenotypic classifications are targeted towards describing the concurring underlying pathologies, without highlighting the most probable ischemic stroke etiology, while causative classifications focus on establishing the most likely cause, neglecting other associated diseases. A judicious use of this two different concepts might improve clinical research as well as daily clinical practice.