Editors’ Note: Dr. Martinez-Ramirez et al. comment on study limitations that might have led to the authors' conclusions in “Microbleeds do not affect rate of cognitive decline in Alzheimer disease.” Dr. Vanacore, in reference to “Neurodegenerative causes of death among retired National Football League players,” raises the 12-fold higher risk of death from ALS in professional Italian soccer players, specifically midfielders, and calls for further cohort studies in other professional athletes. Megan Alcauskas, MD, and Robert C. Griggs, MD
van der Vlies et al.1 found no effect of cerebral microbleeds (MBs) on the rate of cognitive decline in patients with Alzheimer disease (AD). The same cohort previously demonstrated an association between MBs and mortality.2 Therefore, the current findings suggest that this increase in mortality was not a simple reflection of cognitive decline as measured here. However, MBs have been shown to independently affect several cognitive domains in subjects without dementia3,4 and in patients with cerebral small-vessel disease.5
Several limitations may have precluded demonstration of such effects in patients with AD: a small number of patients with lobar MBs, the use of a relatively crude measure of cognitive decline, or the overwhelming effect of AD pathology on cognition compared with any presumed MB-related effects.
The mechanisms by which MBs may affect cognition are still unclear. Do MBs exert their effects through direct tissue disruption or are they merely markers of accompanying cerebrovascular pathologies such as cerebral amyloid angiopathy? If MBs have direct effects on cognitive function, it is possible that specific anatomical location of MBs would have a role.4,5 Further larger studies in elderly patients with cognitive impairment may help answer some of these questions.
- © 2013 American Academy of Neurology
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