[Risk factors and mechanisms of post-stroke dementia]

Stroke significantly increases the risk of dementia in subjects aged 55 years or more. Twenty to 25 p. 100 of patients are demented 5 years after a stroke. Age and supratentorial location of the vascular lesion are risk factors for post-stroke dementia. Volume, left side of the lesion, large middle cerebral artery infarction, lesions of the frontal lobe, second stroke, diabetes, aphasia, clinical features expressing the severity of the stroke event in the acute phase, mitral valve prolapse, atrial fibrillation, depression, concomitant hypoxic/ischemic disorders, and white matter changes have also been found as predictors of dementia. There are many different mechanisms of vascular pathology that may lead to dementia: ischemic or hemorrhagic lesions, large vessel disease including multi-infarct and strategic single infarct, small-vessel disease including lacunes and white matter changes, hypoperfusion.... Post-stroke dementia may not be due only to vascular lesion. Some post-stroke dementias have a progressive onset and course. The cognitive decline may pre-exist to the stroke, even when a dementia is not diagnosed. This suggests a degenerative process. Alzheimer's disease is frequent in ages when the majority of strokes occur. Alzheimer's and vascular diseases share common risk factors such as age, APOE4, hypertension, and smoking. Patients with low MMS scores and AD patients are at risk for stroke. Moreover, white matter changes are associated with stroke and Alzheimer's disease and may contribute to the cognitive decline. Many post-stroke dementias could be multifactorial. Even when vascular lesions and degenerative changes (mainly Alzheimer changes) are not severe enough, no their own, to be the cause of dementia, their summation may reduce the preclinical stage of the degenerative process.