Cognitive Impairment, Dementia and Mortality

Two interesting research articles this week about cognition and Alzheimer’s disease. One in the Archives of General Psychiatry that found that cognitive markers at baseline were more robust predictors of conversion than most biomarkers. And a study in the Annals of Internal Medicine¬† reports that cognitive impairment, even when detected at an early, mild stage, is a significant predictor of decreased life expectancy.

Research in the Archives of General Psychiatry set out to determine the discriminative utility of different classes of biomarkers and cognitive markers by examining their ability to predict a change in diagnostic status from mild cognitive impairment to Alzheimer disease.

Using the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database, researchers evaluated patients with mild cognitive impairment who converted to Alzheimer disease (n = 116) and those who did not convert (n = 204) within a 2-year period. The investigators used a range of tests to assess cognition and functional abilities. They also took cerebrospinal fluid samples at the beginning of the study and every year for two years. Blood samples were also taken when the study began to evaluate for specific genetic variations which are linked to Alzheimer’s disease. Cortical thickness and brain volume information was gathered from from MRI (magnetic resonance imaging) results included in the ADNI database on study participants.

Interestingly enough, changes in functional activity scores seemed to show a greater rate of decline in the participants than changes in biomarkers. The researchers concluded that “cognitive markers at baseline were more robust predictors of conversion than most biomarkers. Longitudinal analyses suggested that conversion appeared to be driven less by changes in the neurobiologic trajectory of the disease than by a sharp decline in functional ability and, to a lesser extent, by declines in executive function.”

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According to a new, long-term study from Regenstrief Institute and Indiana University researchers, and published in the Archives of Internal Medicine this week, 3957 older adults aged 60 to 102 years were screened for cognitive impairment at scheduled primary care appointments. Researchers wanted to determine  whether cognitive impairment is independently associated with increased long-term mortality in primary care patients aged 60 years and older.

At baseline, patients were screened for cognitive impairment and were categorized into groups with no, mild, or moderate to severe cognitive impairment. Baseline data from comprehensive electronic health records were linked with vital status obtained from the National Death Index. The patients were followed for 13 years.

At screening, 3,157 had no cognitive impairment, 533 had mild impairment, and 267 had moderate to severe impairment. During follow-up, 57 percent of patients with no impairment died, compared with 68 percent of those with mild impairment and 79 percent of those with moderate to severe impairment. Median survival time was 138 months for patients with no impairment, 106 months for those with mild impairment, and 63 months for those with moderate to severe impairment.

The study found that cognitive impairment, even when detected at an early, mild stage, is a significant predictor of decreased life expectancy. And, the authors point out that at the moderate to severe stages cognitive impairment has an impact on life expectancy similar to chronic conditions such as diabetes or chronic heart failure.

According to the researchers, these findings have important clinical and prognostic implications beyond dementia detection, treatment and support for affected patients and their families. Reduced life expectancy in patients with cognitive impairment should be factored into medical decisions, such as advance care planning, cancer screening and prescribing of medications, especially in patients with severe impairment, the authors state.

Given that the magnitude of the risk of mild and moderate to severe cognitive impairment is similar to that of many life-limiting diseases, as well as the ease of indentifying cognitive impairment by using a short screening tool, recognition of cognitive impairment in primary care practices should be given a higher priority, the study concludes.

This study was supported by the Agency for Healthcare Research and Quality (AHRQ)

References:

Utility of Combinations of Biomarkers, Cognitive Markers, and Risk Factors to Predict Conversion From Mild Cognitive Impairment to Alzheimer Disease in Patients in the Alzheimer’s Disease Neuroimaging Initiative
Arch Gen Psychiatry. 2011;68(9):961-969

Cognitive Impairment: An Independent Predictor of Excess Mortality. A Cohort Study
Ann Intern Med. 2011;5;155(5):300-308.