More Data Tie Cognitive Decline to Microbleeds

Not only the extent but also the location of cerebral microbleeds could indicate an increased risk for both cognitive decline and dementia, researchers said.

Among more than 3,000 participants in the prospective Rotterdam Study, the presence of four or more microbleeds at baseline MRI imaging was associated with significant declines over the next 6 years in six of nine measures of cognitive function, reported Saloua Akoudad MD, PhD, of University Medical Center Rotterdam, and colleagues.

Lobar microbleeds in particular were associated with lower scores on tests related to executive functions (mean difference in Z score -0.31; 95% CI -0.51 to -0.11; P=0.003), information processing (mean difference in Z score -0.44; 95% CI -0.65 to -0.22; P<0.001), and memory function (mean difference in Z score -0.34; 95% CI -0.64 to -0.03; P=0.03).

Microbleeds detected in other regions of the brain (aside from the lobar region) were associated with a decrease in tests related to information processing and motor speed (mean difference in Z score -0.61; 95% CI -1.05 to -0.17; P=0.007), Akoudad and colleagues reported in JAMA Neurology.

However, it wasn't clear that the microbleeds, or the vascular defects they reflect, actually caused the cognitive decline. The researchers noted that underlying neurodegenerative processes not evaluated in the study could be responsible for both phenomena.

Previous reports have confirmed that microbleeds are common in Alzheimer patients. However, there is a dearth of longitudinal studies that have analyzed microbleeds, and how they relate to cognitive functions, making this study more valuable.

In an accompanying editorial, Philip B. Gorelick, MD, PhD, of Michigan State University and Muhammad U. Farooq, MD, of Mercy Health Hauenstein Neurosciences (both in Grand Rapids, Mich.), pointed out that antithrombotic use -- common in the elderly -- may put patients at extra risk of microbleeds. They noted that doctors will have to be cautious in deciding how to treat patients with cardiovascular conditions that might call for antithrombotic treatment when they also have MRIs showing the presence of multiple microbleeds.

In the longitudinal study, participants underwent baseline exams from 2005 to 2011, and again a mean of 6 years later. Participants were screened for dementia with a three-step protocol, and those who tested positive were further assessed by a neurologist. After the follow-up data was gathered, it was concluded that 72 of the participants had developed dementia, and that the presence of microbleeds was indeed linked to increase risk for the condition.

The overall prevalence of microbleeds among the whole sample was 15.3%. Out of the 3,257 participants included in the analysis, 10.9% (354) were reported to have lobar microbleeds, and 3.8% (123) were reported to have deep or infratentorial microbleeds.

Cognitive tests included the Mini-Mental State Examination, Letter Digit Substitution Test, Word Fluency Test , Stroop test, 15-Word Verbal Learning Test (including immediate, delayed and recognition subtests), and the Purdue Pegboard Test.

Akoudad and colleagues noted the potential for type I errors due to the use of multiple statistical tests. In addition, the technological imaging methods for detecting microbleeds are not flawless.

The authors also conceded that microbleeds could be the result of intense vascular and neurodegenerative diseases, and not necessarily the cause of cognitive deterioration. At this point only correlation, and not causation, has been proven, they stressed.