Delirium Rapidly Accelerates Memory Decline In Alzheimer's Patients

"The cognitive rate of decline was found to be three times more rapid among those Alzheimer's patients who had had an episode of delirium than among those who did not have such a setback," according to lead author Tamara Fong, MD, a staff neurologist at BIDMC and Assistant Scientist at the Institute for Aging Research, Hebrew Senior Life. "In other words, the amount of decline you might expect to see in an Alzheimer's patient over the course of 18 months would be accelerated to 12 months following an episode of delirium."

Alzheimer's disease is an irreversible, progress form of dementia that gradually destroys a person's ability to carry out even the simplest of tasks, and affects as many as 4.5 million individuals in the U.S. according to figures from the National Institute on Aging. There is currently no cure for Alzheimer's disease.

Delirium, on the other hand, is a potentially preventable condition, which often develops following a medical disturbance, surgery or infection and is estimated to affect between 14 percent and 56 percent of all hospitalized elderly patients.

The investigators performed a secondary analysis of data gathered from 408 patients examined between 1991 and 2006 at the Massachusetts Alzheimer's Disease Research Center (MADRC). Over this 15-year period, MADRC staff conducted a number of memory tests on patients. Testing was done on at least three occasions, separated by intervals of approximately six months. Seventy-two of the participants developed delirium during the course of the study.

In their final analysis, the authors found that among patients who developed delirium, the average decline on cognitive tests was 2.5 points per year at the beginning of the study; following an episode of delirium, decline nearly doubled to 4.9 points per year.

"Although each dementia patient declines at his or her own individual rate, the results of our study tell us that this rate can increase three-fold following an episode of delirium," says Fong. "As an example, suppose an Alzheimer's patient begins with mild symptoms, such as forgetting appointments or details of conversations, but over a period of the next 18 months, loses the ability to identify relatives, becomes lost while driving familiar routes, or can no longer balance a checkbook or manage financial transactions. This same patient, were he or she to experience an episode of delirium, might experience this same rate of decline in only 12 months."

While further investigations are needed to determine the mechanism behind this turn-of-events, Fong explains that delirium may, in fact, be a key link in a chain of events that results in injury to brain cells. "Older patients may be at greater risk of developing delirium – particularly in the hospital setting – because they tend to have less 'reserve' or ability to compensate in settings of increased stress. Consequently, infections, new medications and other stressors put the patient at risk for delirium."

All elderly patients, but particularly patients who have already been diagnosed with Alzheimer's disease, can benefit from a number of preventive measures if they are hospitalized, notes Fong.

"As much as possible, it's important to try and orient the patient to his or her surroundings [i.e. frequently remind the patient that he or she is in the hospital], to allow for as much uninterrupted sleep as possible by not waking patients to take vital signs or do blood draws at night, and to get patients out of bed and walking as soon as their medical condition allows," notes Fong. Also, important, she adds, is to avoid use of unnecessary medications.

"Twenty percent of all elderly patients who develop delirium go on to experience complications, whether it's a prolonged hospital stay, a move to a rehabilitation center or long-term care facility, or even death," notes Fong. "Our current study now shows that delirium can also adversely impact the state of cognitive decline in patients with Alzheimer's disease. Because up to 40 percent of delirium episodes can be prevented, taking steps to avoid delirium could result in significant improvements."

The findings are reported in the May 5 issue of the journal Neurology.

This study was funded, in part, by grants from the Massachusetts Alzheimer's Disease Research Center, the National Institute on Aging, and the Alzheimer's Association, and the VA Rehabilitation Career Development Award.

Study coauthors include BIDMC investigators Edward Marcantonio and Sharon Inouye; Hebrew Senior Life investigators Richard Jones, P. Shi, J.L. Rudolph, F.M. Yang and Douglas Kiely; and L. Yap of Massachusetts General Hospital.