Delirium increases dementia risk and mortality in older patients

Delirium is a strong risk factor for dementia and death among older people, finds the largest study of its kind published by The BMJ today. 

The findings show that, among hospital patients with at least one episode of delirium, the risk of receiving a new dementia diagnosis was three times higher than for patients without delirium and each additional episode of delirium increased that risk by 20%. 

The researchers say their findings support the theory that delirium has a strong independent effect on dementia risk in this clinical population.

Delirium is a sudden change in a person's usual mental state. Symptoms include agitation, confusion or being unable to stay focused when awake. Delirium is much more common in hospital patients and older people. 

Previous observational studies have suggested an association between delirium and subsequent dementia, but study limitations leave the size and nature of this relationship unclear.

Yet as the global burden of dementia increases, it is of critical importance to confirm the extent to which delirium is a potentially modifiable risk factor.

To try and address these uncertainties, researchers in Australia analysed data from 626,467 patients aged 65 years and older with no dementia diagnosis who were admitted to hospital in New South Wales between January 2009 and December 2014.

Of these patients, 55,211 had at least one recorded episode of delirium and were matched to another 55,211 patients without delirium by age, sex, frailty, reason for being in hospital, length of stay in hospital and length of stay in the intensive care unit.

These 110,422 patients (average age 83; 52% women) were then followed-up for five years to see how many of them were diagnosed with dementia.

Collectively, 58% (63,929) of patients died and 17% (19,117) had a newly reported dementia diagnosis over the follow-up period.

The researchers found that patients with delirium had a 39% higher risk of death and three times the risk of being diagnosed with dementia than patients without delirium.

The relationship between delirium and dementia was stronger in men than women and each additional episode of delirium was associated with a 20% increased risk of developing dementia (a dose-response relationship).

These are observational findings, so cannot establish cause, and the authors acknowledge that hospital data may not be completely accurate. Nor can they rule out the possibility that other unmeasured factors may have affected their results.

However, this was a large, well-designed study with a long follow-up period, and results were similar after further analyses to test the strength of the associations, suggesting that they are robust.

"While our results are consistent with the hypothesis that delirium plays a causative part in dementia, they are not conclusive owing to the fundamental limitations of observational studies in determining causality," they write. "Nevertheless, the results of this study provide valuable insights because prospective randomized controlled trials are unlikely to be conducted."

"Delirium is a factor that could triple a person's risk of dementia. Therefore, delirium prevention and treatment are opportunities to reduce dementia burden globally," they conclude.