Pathology

Disease

Clinical psychology

Neuroinflammation

Psychiatry

Etiology

Distress

Cognition

Intensive care medicine

Psychology

Neurocognitive

Psychological intervention

Schizophrenia (object-oriented programming)

Organic mental disorders

Delirium

Antipsychotic

Medicine

Nature Reviews Disease Primers

Delirium, a syndrome characterized by an acute change in attention, awareness and cognition, is caused by a medical condition that cannot be better explained by a pre-existing neurocognitive disorder. Multiple predisposing factors (for example, pre-existing cognitive impairment) and precipitating factors (for example, urinary tract infection) for delirium have been described, with most patients having both types. Because multiple factors are implicated in the aetiology of delirium, there are likely several neurobiological processes that contribute to delirium pathogenesis, including neuroinflammation, brain vascular dysfunction, altered brain metabolism, neurotransmitter imbalance and impaired neuronal network connectivity. The Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) is the most commonly used diagnostic system upon which a reference standard diagnosis is made, although many other delirium screening tools have been developed given the impracticality of using the DSM-5 in many settings. Pharmacological treatments for delirium (such as antipsychotic drugs) are not effective, reflecting substantial gaps in our understanding of its pathophysiology. Currently, the best management strategies are multidomain interventions that focus on treating precipitating conditions, medication review, managing distress, mitigating complications and maintaining engagement to environmental issues. The effective implementation of delirium detection, treatment and prevention strategies remains a major challenge for health-care organizations globally. Delirium is a severe neuropsychiatric syndrome characterized by an acute change in attention, awareness and cognition and is caused by various medical conditions. This Primer reviews the epidemiology, pathophysiology, diagnosis and classification of delirium as well as its management approaches and discusses future directions in delirium research and treatment.