Original Paper

New Approach to Stroke Subtyping: The A-S-C-O (Phenotypic) Classification of Stroke
P. Amarenco^a, J. Bogousslavsky^b, L.R. Caplan^c, G.A. Donnan^d, M.G. Hennerici<sup>e

a</sup>Department of Neurology and Stroke Center, INSERM U-698 and Paris-Diderot University, Bichat University Hospital, Paris, France;
^bDepartment of Neurology, Genolier Swiss Medical Network, Valmont-Genolier, Glion-sur-Montreux, Switzerland;
^cDivision of Cerebrovascular/Stroke, Beth Israel Deaconess Medical Center, Boston, Mass., USA;
^dNational Stroke Research Institute, Austin Health, University of Melbourne, Melbourne, Vic., Australia;
^eDepartment of Neurology, University of Heidelberg, Universitätsklinikum Mannheim, Mannheim, Germany

Address of Corresponding Author

Cerebrovasc Dis 2009;27:502-508 (DOI: 10.1159/000210433)

  Key Words

• Stroke
• Subtype
• Severity

  Abstract

We now propose a new approach to stroke subtyping. The concept is to introduce a complete 'stroke phenotyping' classification (i.e. stroke etiology and the presence of all underlying diseases, divided by grade of severity) as distinguished from past classifications that subtype strokes by characterizing only the most likely cause(s) of stroke. In this phenotype-based classification, every patient is characterized by A-S-C-O: A for atherosclerosis, S for small vessel disease, C for cardiac source, O for other cause. Each of the 4 phenotypes is graded 1, 2, or 3. One for 'definitely a potential cause of the index stroke', 2 for 'causality uncertain', 3 for 'unlikely a direct cause of the index stroke (but disease is present)'. When the disease is completely absent, the grade is 0; when grading is not possible due to insufficient work-up, the grade is 9. For example, a patient with a 70% ipsilateral symptomatic stenosis, leukoaraiosis, atrial fibrillation, and platelet count of 700,000/mm³ would be classified as A1-S3-C1-O3. The same patient with a 70% ipsilateral stenosis, no brain imaging, normal ECG, and normal cardiac imaging would be identified as A1-S9-C0-O3. By introducing the 'level of diagnostic evidence', this classification recognizes the completeness, the quality, and the timing of the evaluation to grade the underlying diseases. Diagnostic evidence is graded in levels A, B, or C: A for direct demonstration by gold-standard diagnostic tests or criteria, B for indirect evidence or less sensitive or specific tests or criteria, and C for weak evidence in the absence of specific tests or criteria. With this new way of classifying patients, no information is neglected when the diagnosis is made, treatment can be adapted to the observed phenotypes and the most likely etiology (e.g. grade 1 in 1 of the 4 A-S-C-O phenotypes), and analyses in clinical research can be based on 1 of the 4 phenotypes (e.g. for genetic analysis purpose), while clinical trials can focus on 1 or several of these 4 phenotypes (e.g. focus on patients A1-A2-A3).

Copyright © 2009 S. Karger AG, Basel

  Author Contacts

Prof. Pierre Amarenco, MD
Department of Neurology and Stroke Centre, Bichat University Hospital
46, rue Henri Huchard
FR-75018 Paris (France)
Tel. +33 1 4025 8726, Fax +33 1 4025 7198, E-Mail pierre.amarenco@bch.aphp.fr

  Article Information

Received: February 2, 2009
Accepted: February 2, 2009
Published online: April 3, 2009
Number of Print Pages : 7
Number of Figures : 1, Number of Tables : 3, Number of References : 1