LONDON – Small infarct-like brain lesions have long been ignored in both research and clinical settings, but an ongoing analysis of an observational cohort shows that they can be just as cognitively damaging as large infarcts. Having both is a serious one-two punch to thinking and memory.
At less than 3 mm, infarct-like lesions (ILL) may be tiny, but, over 20 years, they exerted exactly the same deleterious effect on cognition as lesions 3 mm or larger,
When neuroradiologists began to look at brain infarcts several decades ago, they used then state-of-the-art 1.5 Tesla MRI. As infarct description and classification evolved, anything measuring smaller than 3 mm was classified as an infarct-like lesion and anything 3 mm or larger as a large infarct. There was some concern that readers would confuse the ILLs with perivascular spaces and flag these normal voids as pathological changes, Dr. Windham said. As a result, research studies have always excluded them. Since they’re usually associated with silent events, without any clinical signs or symptoms, they’ve been clinically disregarded as well, adding to the perception that they have little long-term impact.
However, in 2015, Dr. Windham and her team proved this perception incorrect, at least when it came to stroke and stroke mortality. Using the large cohort, they that ILLs alone tripled the risk of both a stroke and stroke mortality. Patients who had both ILLs and large infarcts were nine times more likely to have a stroke and seven times more likely to die from a stroke than were patients who had no lesions.
Dr. Windham used the same ARIC cohort in the 20-year cognition study. Begun in 1987, ARIC enrolled 15,800 middle-aged adults who have been followed regularly with physical and neurocognitive testing. Its goals are largely to investigate the natural history and multiple risk factors of cardiovascular and cerebrovascular disease. In 1993, subjects who had not experienced a stroke also had a brain MRI to add more detail to the study. The investigators also have performed cognitive assessments of a large number of participants five times since 1993 on measures of delayed word recall, digit symbol substitution, and word fluency. The outcome was the change in the composite Z-score over time.
The cognition study comprised 1,881 who had brain MRI and the full five cognitive assessments over a 20-year period. The participants were stratified as having no infarcts (1,611), only ILLs (50) or large infarcts (185), or both lesions (35).
At baseline, these subjects had a mean age of 63 years, 17% had diabetes, and 48% had hypertension. About one-third were positive for an ApoE e4 allele. The mean white matter intensity score was 1.4.
“In general, everyone in the cohort had some decline in cognitive function as they got older,” Dr. Windham said. But, a striking observation was that those with ILLs only and those with large lesions only had virtually identical decline slopes over the 20-year follow-up. The change from baseline in global Z-score was 0.18 standard deviations for the ILL-only group and 0.24 standard deviations for the large infarct group. For those with both lesions, the change from baseline was 0.62.
“At the end of 20 years, those with no lesion burden declined 1.3 standard deviations from baseline, those with only ILLs declined 1.5 standard deviations, and those with large infarcts, 1.6 standard deviations,” Dr. Windham said. “But, subjects who had both lesions declined 2.5 standard deviations from baseline. This is equivalent to adding 27 years of aging. The effect of having both was nearly four times greater than [that of] having only large lesions, which, up until now, have been the only ones read on MRI in either clinical practice or in research. Overall, our findings confirm that the relationship of ILLs to cognition is very similar that of large infarcts.
“The presence of midlife ILLs appears to amplify the effect of large infarcts on cognition, and we hypothesize that this process may represent vascular disease at midlife. We may also be able to identify people at high risk of cognitive decline or even dementia at midlife. I also think that we need to be rethinking how we read MRIs. Stopping at the 3-mm threshold may be too conservative. We should be looking at other studies on the consequences of these small lesions,” she said.
Dr. Windham had no financial disclosures.