Delirium is a neuropsychiatric syndrome, characterized by an acute change in mental status with a fluctuating course of symptoms, that affects almost 50% of people aged 65 years or older, admitted to hospital. Delirium is associated with negative outcomes, including increased risk of mortality, cognitive and functional decline. In 50% of the cases, the cause of delirium is multifactorial, resulting from a complex inter-relationship between several predisposing factors (e.g. advanced age, dementia) in highly vulnerable patients that are exposed to precipitating factors (e.g. infections). In this context, cognitive impairment and dementia are important risk factors for delirium, increasing its risk by two to five times, associated with worse outcomes. The underlying brain vulnerability of these patients with dementia may predispose to the development of delirium, as a consequence of insults related to the acute medical disease, medication or environmental factors. On the other hand, delirium may cause permanent neuronal damage, which may lead to the development or worsening of a pre-existing dementia. As a result, delirium and dementia frequently coexist and overlap, challenging differential diagnosis.

The identification of risk factors for delirium, specifically pre-existing cognitive impairment or dementia, in elderly people admitted to hospital is essential to the implementation of preventive strategies that may contribute to the decrease of delirium rates. The present literature review aims to highlight the association between delirium and dementia in elderly people, focusing on diagnosis, pathophysiology, prevention, and management.