As Stroke Decreases, Dementia Increases

Summarized by Robert W. Griffith, MD
June 5, 2006

Summary

Decreased stroke mortality - due to improved treatment methods - is associated with increased vascular dementia in the survivors in later years

Introduction

People who have had a stroke are more likely to develop dementia - several times more likely, in fact. Fortunately, it seems that the frequency of stroke has been decreasing, both in the USA and Europe. One might hope that this would be accompanied by a corresponding decrease in dementia. Scientists at Duke University, North Carolina, have done a study of the changes in stroke admission rates and survival, together with the rates of new dementias. Their findings are reported in the journal Stroke, and we summarize them here.

What was done

Inpatient claims for Medicare funds were used to provide the information for analysis. Over 40,000 US citizens over 65 were surveyed at five intervals between 1982 and 1999. At each survey, a group of approximately 5000 new persons over 65 were added to the whole, to replace the deaths that had occurred after the previous survey.

The stroke patients were identified from the coding used on the Medicare forms. Dementias were also identified in this way, and classified into Alzheimer's disease, vascular dementia, and 'senile' dementia (this class represented mental deterioration without the diagnostic signs of Alzheimer's or vascular dementia).

The rates of occurrence of first stroke and newly diagnosed dementia after stroke were evaluated. Dementia diagnosed before a stroke were excluded from analysis.

What was found

There was only a slight increase in stroke rates during the study period. However, the survival 1 year after a stroke increased significantly from 53% in 1984-1990 to 65% in 1991-1999.

Newly diagnosed dementias increased by 50% form 1984-1990 to 1991-1999. The greatest increase was seen in vascular dementia; increases in Alzheimer's disease and senile dementia were less obvious.

The overall likelihood of dementia occurring was much higher - about 10 times - in the first year after a stroke than in stroke-free persons. For the stroke-free, dementia rates increased over time, but they were mostly of the Alzheimer-type.

What these results may mean

The increase in vascular dementia in individuals with stroke might possibly be linked to the improved survival after their acute cerebrovascular episode. The authors of the study speculate that the decreased mortality was due to more people with greater brain damage surviving, who might be more predisposed to vascular dementia. The similar increases in Alzheimer's disease in those people with and without stroke suggests no obvious role of stroke treatment in precipitating this type of dementia.

More people survived stroke, leading to fewer overall stroke deaths. But this improvement in therapy was accompanied by an increase in vascular dementia. Obviously more research into the actual reasons for this increase is needed; for instance, whether the acute treatment of stroke should be modified to try to lessen the likelihood of dementia developing in the next few years. A challenging research program, indeed!

Source

• Increasing rates of dementia at time of declining mortality from stroke. S. Ukraintseva, F. Sloan, K. Arbeev, A. Yashin, Stroke, 2006, vol. 37, pp. 1155--1159

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