Hospitalization Linked to More Cognitive Decline in Elderly

Pauline Anderson

March 23, 2012

March 23, 2012 — Older adults have a 2.4-fold increase in the rate of cognitive decline after hospitalization, an increased risk that persisted after adjustment for severity of illness and length of hospital stay, according to a new study.

Because cognitive impairment is a major source of disability in older people, learning how cognition is linked to something as common as hospitalization is extremely important, the researchers say.

"Industrialized countries like the U.S. and Canada are experiencing a great aging of the population and so we're expecting an increased prevalence of cognitive disorders," Robert S. Wilson, PhD, professor, neurological sciences and behavioral sciences, Rush University Medical Center, Chicago, Illinois, who led the study, told Medscape Medical News. "Understanding what the consequences of those disorders are and what factors may be contributing to cognitive impairment in old age are major priorities in health care research right now."

The study was published online March 21 in Neurology and will appear in the March 27 issue.

Global Cognition

As part of the longitudinal, population-based Chicago Health and Aging Project, researchers assessed changes in cognitive function among older people. They used a composite of cognitive tests that assessed episodic memory (immediate and delayed recall), executive function, and global cognition (Mini-Mental State Examination).

They also accessed Medicare records of hospitalizations and used the Charlson comorbidity index to determine degree of illness.

The analysis included 1870 patients aged 65 years and older who had brief tests of cognitive function at 3-year intervals. During a mean of more than 9 years, 1335 (71.4%) of these patients were hospitalized at least once. The initial hospitalization occurred a mean of 3.8 years after study onset and lasted a median of 5 days. The mean duration of follow-up after initial hospitalization was 5.7 years.

After controlling for age, sex, race, and education, the study found that the composite measure of global cognition declined a mean of 0.031 unit per year before hospitalization and in those never hospitalized. After hospitalization, the rate accelerated by 0.044 unit to a mean loss of 0.075 unit per year. This corresponds to a more than 2.4-fold increase relative to the decline preceding hospitalization.

With regard to individual cognitive domains, there was a 3.3-fold increase in the rate of episodic memory decline, from a loss of 0.014 unit per year before hospitalization to 0.046 unit per year after hospitalization.

Hospitalization was also robustly related to decline in executive function. Decline in this function increased 1.7-fold, from a loss of 0.053 unit per year before hospitalization to 0.091 unit per year afterward.

These results suggest that cognitive decline after hospitalization is global in nature, say the authors.

Illness Severity

In analyses that controlled for the length of hospital stay and how sick individuals were while in the hospital, the effect was only somewhat diminished. "There was still a substantial effect after accounting for individual differences in how ill they were, so we don't think that this entirely explains the effect, by any means," said Dr. Wilson.

Delirium could play a role in the accelerated cognitive decline in hospitalized older patients. Delirium is common in older patients who are critically ill, and the condition has been associated with sedative drugs and certain medical procedures, said Dr. Wilson. As well, he said, older patients with delirium tend not to do as well cognitively after hospitalization.

However, although delirium may be a factor, "how much of this can really be pinned on delirium per se is hard to say," said Dr. Wilson. He noted that delirium is difficult to define, and that there are subsyndromal versions of the condition.

He stressed that further research is needed to "pin down" the basis of these hospital-related cognitive effects. "We think it's going to be multiple factors that are contributing."

In addition, as the authors noted, only 3% of hospitalizations in the study involved a critical illness but 15% to 20% of older general medical inpatients are estimated to meet the criteria for delirium.

Challenges Ahead

Preventing or reducing loss of cognitive function in the elderly "is a challenge that lies ahead of us," said Dr. Wilson. Efforts could be made to implement more effective primary prevention of medical problems that might minimize hospitalization of the elderly and to improve inpatient and discharge policies and procedures.

"Perhaps we should be rethinking how aggressively we hospitalize older people, particularly older people that have pre-existing cognitive impairment," said Dr. Wilson. "And perhaps we should be treating older people with cognitive impairment when they are hospitalized differently than we are now."

Asked to comment on the study, Laura Banks, MD, co-director of the Monterey Neurological Institute in California, told Medscape Medical News that the study was intriguing and a "good first step" and that it parallels what she observes herself.

"It's consistent with what I see in practice where you have patients who are in their 70s or 80s and are doing okay and then they break a hip, or they get a medication overdose one time, end up in hospital with delirium, and they're never quite the same."

However, said Dr. Banks, cognitive testing of patients in the study was not very frequent and the researchers didn't have very good information about subjects' histories, what caused them to go into the hospital, and what medications they took while in the hospital.

"So this fits in with what I see as a physician; as a scientist, I would like to see more proof."

Dr. Wilson serves as a consulting editor for Aging, Neuropsychology, and Cognition and Psychology and Aging; has served as a consultant to Pain Therapeutics, Inc; and receives research support from National Institutes of Health/National Institute on Aging. Conflict of interest information for other authors appears in the publication. Dr. Banks has disclosed no relevant financial relationships.

Neurology. 2012;78:950-956. Abstract