Larger Volume White Matter Hyperintensities Correlate with Cognitive Decline
White matter hyperintensities are small volumes of damage and scarring in the white matter of the brain, named for the way they appear in MRI images of brain tissue. They can be caused by rupture of small blood vessels, but also by any other localized cause of cell death and inflammation. Greater numbers of white matter hyperintensitives are generally indicative of a higher risk of neurodegenerative conditions and cognitive decline. Interestingly, researchers here note that the correlation with cognitive decline only exists for larger white matter hyperintensities.
The association between white matter integrity and adverse brain health outcomes is well-established. Increased white matter lesion burden has consistently been linked to higher risk of stroke, cognitive impairment, dementia, and mortality in cross-sectional and longitudinal studies involving diverse patient populations and healthy older adult cohorts.
This study investigates the relationship between white matter hyperintensities (WMHs) and longitudinal cognitive decline in older adults. Using data from The Irish Longitudinal Study on Ageing (TILDA), we examined WMH characteristics, including volume, location, and microstructural integrity, in a community-dwelling population of 497 individuals over a six-year period. WMHs were categorised into phenotypes based on their size, fractional anisotropy (FA), and mean diffusivity (MD), with subtypes for periventricular and deep white matter lesions. We hypothesised that larger, microstructurally compromised lesions would be associated with accelerated cognitive decline.
We isolated 11,933 WMHs, with an average of 24 WMHs per individual. Of these lesions, 6,056 (51%) were classified as Low Volume - High FA, 3193 (27%) were classified as Low Volume - Low FA and 2684 (22%) were classified as High Volume, Low FA. Our findings demonstrate that high-volume, low FA deep and periventricular lesions were significantly linked to cognitive decline, whereas small periventricular lesions with near normal microstructural properties do not predict cognitive decline. These results suggest that distinct WMH phenotypes may serve as markers for differential risks of cognitive impairment, providing potential targets for early intervention in at-risk populations.