Delirium

Disease class: Neurocognitive disorders

Also known as acute confusional state. 

 

Definition

A condition of altered consciousness in which there is disorientation (as in a confusional state), incoherent talk and restlessness but with hallucination, illusions or delusions also present.

In some old people, acute confusion is a common effect of physical illness. Elderly people are often referred to as being ‘confused’; unfortunately this term is often inappropriately applied to a wide range of eccentricities of speech and behaviour as if it were a diagnosis. It can be applied to a patient with the early memory loss of dementia– forgetful, disorientated and wandering; to the dejected old person with depression, often termed pseudo-dementia; to the patient whose consciousness is clouded in the delirium of acute illness; to the paranoid deluded sufferer of late-onset schizophrenia; or even to the patient presenting with the acute dysphasia and incoherence of a stroke.

Prescription drugs, such as antidepressants, may contribute to delirium, especially in the elderly.

Source: Black's Medical Dictionary (42nd ed, 2010, ISBN 978-1-4081-0419-4) 

Delirium is a temporary and reversible state.

These patients often appear to have advanced dementia, but unlike dementia, this is rapidly progressive (hours or days) and completely reversible.

It usually occurs in the elderly, the severely ill, and patients in critical care.

Something as simple as a urinary tract infection (UTI) can trigger this in the elderly.

It's probably caused by many factors including inflammatory signals.
It can be seen an organ dysfunction like heart failure or liver failure, except it occurs in the brain and is not immediately life-threatening.

Patients with dementia can also get delirium, and this would present as a rapid, reversible decline, like in any other delirium patient.