Cerebral microbleeds warn of dementia risk

By Lucy Piper

A high cerebral microbleed count increases an individual's risk of cognitive deterioration and dementia, study results indicate.

A high count, calculated to be above four, "may represent a proxy for diffuse vascular and neurodegenerative brain damage, which predisposes to progressive cognitive deterioration", the team reports in JAMA Neurology.

They note that multiple microbleeds affected cognition in all domains, with lobar microbleeds associated with a decline in distinct cognitive domains when compared with microbleeds in other locations.

The prevalence of microbleeds, as detected using magnetic resonance imaging, was 15.3% among 3257 participants of The Rotterdam Study aged an average of 59.6 years who had baseline and follow-up MRI scans available. Lobar microbleeds (with or without cerebellar microbleeds) were detected in 10.9% of participants and deep or infratentorial microbleeds (with or without lobar microbleeds) in 3.8%.

A single microbleed alone was not significantly associated with a decline in cognition; it was at a cutoff of four microbleeds when the researchers saw patients performing significantly worse on a battery of neuropsychological tests 5.9 years later.

The tests included the Mini-Mental State Examination, Letter Digit Substitution Task, World Fluency Test, Stroop Test, 15-word Verbal Learning Test.

Multiple lobar microbleeds were specifically associated with significant declines in executive functions, information processing and memory function, whereas multiple microbleeds in other regions were significantly associated with a decline in information processing and motor speed.

The researchers comment that the cognitive effects are consistent with the predominant location of the microbleeds, but they point out that participants with deep or infratentorial microbleeds often had higher microbleed counts and more mixed microbleed locations.

"Hence, microbleed count per topographic brain region may be more informative than the categorizations per presumed underlying vasculopathy in assessing cognitive deterioration", study researcher M Arfan Ikram (Erasmus MC, University Medical Center, Rotterdam, the Netherlands) and team write.

Among 4841 participants available for assessment of dementia during a mean follow-up of 4.8 years, 72 participants developed dementia, 53 of whom had Alzheimer dementia.

The risk of developing dementia doubled among people with any microbleeds, compared with those with none, after taking into account age and gender, and increased 1.80-fold and 2.39-fold for those with lobar and deep or infratentorial microbleeds, respectively. Similar increases in risk were seen for Alzheimer dementia.

However, significant associations with dementia remained only for any and infratentorial microbleeds when lacunes, intracranial volume and white matter lesion volume were taken into account and there were no significant associations when apolipoprotein ε4 allele status and common cardiovascular risk factors were considered.

In a related editorial, Philip Gorelick (Michigan State University College of Human Medicine, Grand Rapids, USA) and Muhammad Farooq (Mercy Health Hauenstein Neurosciences, Grand Rapids, Michigan) discuss the challenge cerebral microbleeds pose in terms of treatment.

The heightened risk of bleeding makes affected patients poor candidates for antithrombotic therapy, they point out. They recommend that physicians adopt a practical approach when administering these medications to patients with cerebral microbleeds and weigh up the benefits and risks.

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