Types of delirium

Delirium has been categorized into 3 generally accepted subtypes: hyperactive, hypoactive and mixed type.

1. Hyperactive delirium is characterized by an increase in psycho-motor activity and agitated state
2. Hypoactive delirium on the other hand is characterized by an inactive, withdrawn or sluggish appearance with a limited or slowed vocalization(21). Patients with severe hypoactive delirium may have catatonic speech and movements(22).
3. A patient may shift from hyperactive to hypoactive delirium throughout the day or within a delirious episode and this is classified as mixed type delirium(23).

Hypoactive delirium is considered the most common type of delirium however it frequently goes undetected as the patient is quiet and non-disruptive(1). Hypoactive delirium is extremely dangerous and often results in very poor outcomes for the patient. These poor outcomes are usually as a result of the underlying cause not being treated and /or the patient 's immobility which increases their risk of complications such as pneumonia, bedsores, decreased functional capacity and even death.

In addition to the full delirium syndrome (per Confusion Assessment Method) it is possible for patients to display one or more of the symptoms of delirium without fulfilling the full delirium criteria and this is called subsyndromal delirium(24). It is suggested that people displaying subsyndromal symptoms should be managed as if they had delirium and the consequently causes of the change in behaviour investigated and managed(23).

Delirium superimposed on dementia (DSD) is the name given to delirium that develops in a person who has dementia. This condition is significant as it found frequently in older hospitalised patients and the acute change is often attributed to the person's dementia getting worse. Even in patients with dementia if the cause of the delirium is found and successfully treated the delirium can be reversed(43).