Cognitive decline and survival in Alzheimer's disease

To test the association of rate of cognitive decline, an indicator of the severity of the underlying disease process, with risk of death in Alzheimer's disease (AD).

A total of 472 persons with clinically diagnosed AD were recruited from a memory disorders clinic and day care centers in the Chicago area. They completed a uniform clinical evaluation at baseline and a battery of nine cognitive tests at six-month intervals for a mean of about three years. A previously established measure of global cognition was derived from the nine tests.

During follow-up, 168 persons (36%) died. In a proportional hazards model that controlled for age, sex, race, education, and baseline level of cognition, individual rate of global cognitive decline, estimated with least squares regression, was linearly related to mortality risk. Thus, a person declining minimally (increase of 0.04 unit per year, 90th percentile) was 2.7 times less likely to die during the study period than a person declining rapidly (decrease of 0.76 unit per year, 10th percentile). Controlling for baseline disability did not substantially affect results. The association of cognitive decline with mortality was substantially stronger for white persons compared to African Americans and in those with less compared to more education.

The results indicate that the rate at which cognition declines in AD is robustly related to survival.