Basic Epidemiology of Stroke and Risk Assessment

Abstract

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) diplopia 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 seizures. (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.