Clinical aspects of microbleeds in Alzheimer's disease

Microbleeds are small lesions, appearing as black dots on T2-weighted magnetic resonance imaging. They occur frequently in Alzheimer's disease (AD), but the clinical relevance of these radiological observations remains unclear. In this paper an overview is given on currently available evidence on the clinical relevance of microbleeds in AD. The evidence linking microbleeds to severity of cognitive impairment in AD is not unambiguous. From the existing literature, it seems reasonable to conclude that multiple microbleeds negatively impact cognitive performance, but there is less consensus on the importance of location of microbleeds in this respect. Regarding progression of disease, there is hardly any evidence that microbleeds affect disease course in terms of progression to AD in patients with MCI or with respect to rate of cognitive decline in AD patients. This may imply that microbleeds simply do not affect disease course, but an alternative explanation for the negative findings would be that these studies are hampered by selective drop-out, as individuals with many microbleeds have an increased risk of (stroke-related) mortality.