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Delirium is linked to an increased risk of dementia in older patients, according to the largest study of its kind.
The study, published in The BMJ, found that patients with delirium were three times as likely to be diagnosed with dementia than patients without delirium.
The authors say the study highlights that delirium prevention and treatment could reduce the global burden of dementia.
Delirium and dementia: what’s the link?
Delirium, or sudden confusion, is a common condition in older people, with up to one in three people admitted to hospital becoming delirious at some point in their stay.
The most common symptoms are disorientation, unusual thoughts (such as paranoia), poor concentration, memory loss, agitation, drowsiness, restlessness and hallucinations.
There are a variety of factors that can cause delirium such as infections, constipation and dehydration. Delerium is therefore often preventable and can be treated effectively depending on the cause.
While previous observational studies have suggested an association between delirium and subsequent dementia, study limitations leave the size and nature of this relationship unclear.
Patient with delirium has increased mortality risk
The authors therefore set out to address this gap by analysing data from 626,467 patients admitted to hospital in New South Wales.
Between January 2009 and December 2014, 55,211 had at least one recorded episode of delirium. These patients were then matched to 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.
During the five year follow up period, 58% of patients died and 17% had a newly reported dementia diagnosis.
The researchers found that patients with dementia had a 39% higher risk of death and were three times as likely to be 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.
Prevention and treatment interventions could reduce dementia incidence
While the study is observational and there were various limitations, the authors say the study was well designed with a long follow-up period, and further analysis found the results to be robust.
The authors conclude: “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.
“Nevertheless, the results of this study provide valuable insights because prospective randomised 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.”