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  • Print publication year: 2009
  • Online publication date: May 2010

5 - Basic epidemiology of stroke and risk assessment

from Section II - Clinical epidemiology and risk factors


Definition of stroke

In epidemiological studies, stroke is defined by clinical findings and symptoms [1]: rapidly developed signs of focal (or global) disturbance of cerebral function lasting more than 24 hours (unless interrupted by surgery or death), with no apparent cause other than a vascular origin. This approach is supplemented with neuroimaging but even with advanced imaging techniques the diagnosis is based on clinical signs. Therefore, precise definitions of clinical signs are needed. WHO definitions are [1]:

Definite focal signs:

unilateral or bilateral motor impairment (including dyscoordination)

unilateral or bilateral sensory impairment

aphasis/dysphasis (non-fluent speech)

hemianopia (half-sided impairment of visual fields)


forced gaze (conjugate deviation)

dysphagia of acute onset

apraxia of acute onset

ataxia of acute onset

perception deficit of acute onset.

Not acceptable as sole evidence of focal dysfunction:

dizziness, vertigo

localized headache

blurred vision of both eyes

dysarthria (slurred speech)

impaired cognitive function (including confusion)

impaired consciousness


(Although strokes can present in this way, these signs are not specific and cannot therefore be accepted as definite evidence of stroke.)

Neuroimaging studies are needed for classification of stroke by subtypes: subarachnoid hemorrhage, intracerebral hemorrhage and brain infarction (necrosis). Although there may be large variations in stroke subtype distributions between populations, thrombotic and embolic strokes are responsible for about 80–85% of all strokes in the Indo-European populations, and as low as 65% in some Asian populations. Subarachnoid hemorrhage represents 5–10% of all strokes, and occurs more often in younger subjects, while both intracerebral and especially thrombotic and embolic stroke increase markedly with age.

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