Dr. Bowler of the Royal Free Hospital in London has no relevant financial relationships to disclose.)
Dr. Hachinski of the University of Western Ontario and Director of the John P Roberts Research Institute has no relevant financial relationships to disclose.)
This article includes discussion of subcortical vascular cognitive impairment, subcortical vascular dementia, Binswanger disease, and leukoaraiosis. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Subcortical vascular cognitive impairment, characterized by subcortical and executive cognitive dysfunction, is now recognized to be the most common form of vascular cognitive impairment. It arises on the basis of small vessel cerebrovascular disease, in turn, causing lacunar infarcts and ischemic damage to the deep white matter. Most importantly, the underlying etiologies are those of well-recognized vascular risk factors, and this is, therefore, a form of cognitive impairment that is amenable to prevention as well as symptomatic relief.
• Subcortical vascular cognitive impairment is the commonest form of vascular cognitive impairment.
• The most severe cognitive deficits are frontal and executive.
• Seventy percent of the risk is inherited.
• Progression is slow early on but becomes more rapid, with increasing severity.
• There is an association between subcortical vascular cognitive impairment, microhemorrhage, and intracerebral hemorrhage.
Historical note and terminology
Subcortical vascular cognitive impairment is now recognized to be the commonest form of vascular cognitive impairment, its clinical pattern, risk factors, and imaging features being sufficiently consistent for it to be considered an entity for the purposes of diagnosis, clinical trials, and management. It is recognized as subcortical vascular dementia in the International Classification of Diseases, 10th revision (World Health Organization 1993).
Its history dates back to the now outdated concept of Binswanger disease, which has been superseded by the modern concept of subcortical vascular cognitive impairment.
Significant small vessel disease was rarely reported before the arrival of CT scanning and MRI. Throughout the last 2 decades of the twentieth century, there were numerous reports of "Binswanger disease" diagnosed solely by the appearance of extensive white matter changes on neuroimaging without clinical correlates. This is now recognized to be inappropriate because leukoaraiosis without readily apparent clinical correlates is very common in the elderly and the term “leukoaraiosis” should be used in describing such imaging findings (Hachinski et al 1987).
Leukoaraiosis can be associated with neurologic signs and psychological deficits, particularly the attention and speed components of executive function. Initial work suggested that only CT-demonstrated leukoaraiosis had clinical correlates, the interpretation being that MRI, a more sensitive tool, was detecting numerous asymptomatic lesions. That more than 90% of elderly individuals have some degree of leukoaraiosis without necessarily being demented was taken to support this. However, detailed neuropsychological assessment has shown that subtle, predominantly subcortical deficits are associated with leukoaraiosis in the absence of dementia and in apparently normal-aged subjects (Dong et al 2015). Longitudinal studies have also demonstrated a correlation between increasing leukoaraiosis and declining cognition (Benedictus et al 2015). These changes are closely associated with hypertension and other vascular risk factors, and these findings, along with the close association between lacunar infarcts and hypertension, have led to the realization that subcortical vascular cognitive impairment begins with mild leukoaraiosis and may progress to advanced subcortical vascular dementia with an underlying pathology comprising not only leukoaraiosis but incomplete infarcts and lacunar infarcts in the deep white matter. This is the single commonest form of vascular cognitive impairment, accounting for 40% of all cases.
Early work confused the cognitive impairment of small-vessel cerebrovascular disease with Alzheimer disease, but this is now well recognized to be inappropriate. Consequently, case identification should be based on predominant frontal and executive cognitive impairment rather than memory. Following from this, the use of the mini mental state examination (MMSE) is inappropriate as the MMSE is insensitive for frontal and executive deficits. It should not be used in rating or diagnosing subcortical vascular cognitive impairment. Tests including elements directed at frontal and executive functions are more appropriate, suitable components, including CLOX, EXIT25, trail making, and digit symbol substitution. Some validation data now exist for the Montreal Cognitive Assessment (MoCA) (Pendlebury et al 2010; Webb et al 2014; Pasi et al 2015; Zamboni et al 2017) and the Addenbrooke's Cognitive Examination (revised edition) (Pendlebury et al 2012). Arbitrary radiological diagnostic criteria should not be used as there are no validated criteria.
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