BACKGROUND: Depression is the most prevalent affective syndrome in old age. Delirium is a common and serious adverse event in elderly patients and is associated with significant cognitive and functional decline and early institutionalisation. Both disorders have shared symptoms and signs. Recent studies suggest that depression is an independent risk factor for delirium, and depression symptoms may also represent sequels of delirium. It is important to identify patients at risk of delirium, in order to apply preventive strategies and to address the consequences of incident delirium. In this narrative review we discuss the complex relationship between depression and delirium in old age.

METHODS: A literature search was conducted using following databases: PsycINFO, Embase, PubMed, Google scolar, Web of science and AgeLine using key words “delirium”, “depression”, “overlap" and "risk factor”.

MAIN FINDINGS: Delirium and depression are complex psychiatric syndromes that are common in old age and associated with poor outcomes. This study gives a general overview about the relationship between depression and delirium. Prior depression is not a rare finding in patients suffering from delirium, and depressive symptoms are frequently observed as sequel of delirium. If delirium occurs, differential diagnosis may be particularly challenging in people with depression. Studies suggest similar pathophysiology, such as disturbances in inflammatory and stress responses. Accurate detection of depression and delirium is a key target to achieve improvement of outcomes and to provide optimal healthcare.

CONCLUSION: The literature suggests an inter-relationship between depression and delirium. Symptoms of depression may contribute an increased risk of delirium and delirium may be a predictor of depression. However, the relationships between the two conditions regarding common underlying pathomechanisms and clinical aspects remain imprecisely defined and requires more study.