Delirium is a common, serious, often fatal disorder affecting as many as 50 percent of older people during the course of surgery or hospitalization and costs more than $164 billion per year. However, until now, the relationship between delirium and long-term cognitive decline has not been well explored.
Researchers from Harvard Medical School and Hebrew SeniorLife Institute for Aging Research (IFAR) have found increasing evidence that delirium in older surgical patients may be associated with long-term cognitive decline. Findings from the study are published in the July 2016 issue of Alzheimer’s & Dementia.
The study, conducted in collaboration with Beth Israel Deaconess Medical Center, Brown University and Northeastern University, examined the trajectory of short-term and long-term cognitive decline in patients who experienced delirium for 36 months following a surgery.
Delirium occurred in 134 of the original 560 participants in the study. Both groups of participants, those who experienced delirium and those who did not, showed a significant cognitive decline at one month, followed by a recovery above baseline at two months and then a gradual decline for the next 34 months. The 560 participants in the study were aged 70 years or older, had no previous signs of dementia and were scheduled to undergo surgery with an anticipated length of hospital stay of three days or greater.
The delirium group, however, had a significantly greater decline at one month compared to those without delirium. Although they too recovered at two months, this group had a more significant decline after the two- month mark than the non-delirium group. Beyond two months, both groups declined on average, but the delirium group declined significantly more. When researchers compared changes from baseline to 36 months, there was no significant change in the group that did not experience delirium, but there was a marked decline in the group that did.
According to the researchers, the fact that both the delirium and non-delirium groups suffered cognitive decline at month one, and then a return to baseline at month two, likely represents the immediate impact of events such as anesthesia, surgery and hospitalization. However, the higher rate of cognitive decline after month one in those with delirium suggests that delirium may set off a cascade of events that lead to progressive, long-lasting effects. Or, it is alternatively possible that delirium is associated with a pre-existing higher rate of cognitive decline that is not detectable at baseline. In either case, delirium may serve as a marker for seniors with poor cognitive reserve.
“This study is highly significant in demonstrating that delirium is associated with subsequent long-term cognitive decline at a pace similar to that of mild cognitive impairment, even in those with normal cognitive function at baseline,” says Sharon Inouye, HMS professor of medicine at Beth Israel Deaconess and director of the IFAR Aging Brain Center at Hebrew SeniorLife. “Whether or not delirium is causative, it identifies those at risk for subsequent cognitive decline and warrants both close clinical follow-up and preventive interventions.”