Severe strokes significantly increase the risk of progressive dementia

As stroke severity increases, the risk of progressive cognitive decline and dementia substantially escalates, according to a national study led by Michigan Medicine researchers.

People with the most severe strokes had five times higher odds of developing dementia and showed cognitive decline equivalent to being more than two years older at baseline compared with people who did not have a stroke. 

The results are published in JAMA Network Open. 

"Stroke severity strongly affects thinking and memory after stroke," said senior author Deborah A. Levine, M.D., M.P.H., professor of internal medicine and neurology at the University of Michigan Medical School.

"Our findings highlight the need to closely monitor cognition and aggressively treat dementia risk factors in all stroke survivors, especially those with severe strokes."

The research team analyzed health care data from more than 42,000 American adults - including approximately 1,500 stroke survivors - who were followed for up to 30 years. 

Dementia risk increased with stroke severity. Compared with people who did not have a stroke, dementia risk was about twice as high after a minor stroke, three times higher after a moderate stroke and five times higher after a severe stroke.

People without stroke showed some age-related cognitive decline over time. But stroke survivors had faster long-term declines in overall cognition, memory and executive function - and the declines were greater with more severe strokes.

On average, survivors of mild-to-moderate stroke declined as if they were 1.8 years older cognitively at baseline, and survivors of moderate-to-severe stroke declined as if they were 2.6 years older. 

Cognitive impairment is not limited to people with moderate or severe strokes; we also see it after mild strokes, so all survivors are at risk and should be monitored."

Mellanie V. Springer, M.D., M.S., co-author and Thomas H. and Susan C. Brown Early Career Professor of Neurology at U-M Medical School

"As stroke severity increases, structural and network damage also increase. This reduces the cognitive reserve and leaves the brain less able to compensate for the stroke itself, normal age-related decline and ongoing injury from vascular risk factors." 

Small vessel disease, neurodegeneration (including Alzheimer's disease) and chronic inflammation may also contribute to cognitive decline and dementia after stroke. 

Researchers say more studies are needed to better understand these mechanisms and to test treatments to prevent poststroke dementia and cognitive decline, including strategies that target blood pressure and glucose control.

Levine's team previously reported that higher glucose levels after stroke are linked to faster poststroke cognitive decline. 

"The best ways to prevent poststroke dementia and cognitive decline are to prevent first and second strokes," Levine said. 

"That means controlling blood pressure, glucose and cholesterol to optimal levels, and taking an anticoagulant when atrial fibrillation is present, as recommended."