Neuroscience Clerkship

DELIRIUM vs. DEMENTIA

Dementia and delirium are common conditions seen by physicians in all medical specialities. The prevalence of dementia increases from 1% at the age of 60 to about 30- 50% by the age of 85. Likewise, delirium is present in 15-20% of all hospitalized patients over the age of 55. Delirium may be the manifestation of a potentially life-threatening underlying condition. Patients with a preexisting dementia or cognitive impairment are especially prone to delirium. Thus, it is important for the clinician to understand both dementia and delirium and be able to differentiate these conditions from each other.

One of the key findings in dementia is that the content of thought, but not the level of consciousness is affected.

According to the DSM-IV criteria, the diagnosis of dementia is based on:

• The development of multiple cognitive deficits manifested by:

Memory impairment

One or more of the following:

◊ Aphasia

◊ Apraxia

◊ Agnosia

• Disturbance of executive functioning

• Cognitive deficits cause significant social and occupational impairment and represent a significant decline from a previous level of functioning

• The deficits are not the result of delirium

Delirium, often referred to as an “acute confusional state,” is an acute, usually reversible state of fluctuating consciousness. Attention is characteristically poor. It usually develops over a short period of time. The cause is usually a toxic or metabolic disturbance. The DSM-IV criteria for the diagnosis of delirium are:

• Disturbance of consciousness with reduced ability to focus, sustain or shift attention

• The change in cognition or perceptual disturbances is not due to dementia

• The disturbance develops over a short period of time (hours to days) and fluctuates during the course of the day

• There is clinical evidence that the disturbance is caused by a general medical condition and/or substance use or withdrawal

Common Causes of Delirium from the Merck Manual of Diagnosis and Treatment:

In addition to the causes listed above, several other factors are involved that may predispose to delirium.  These includes conditions that reduce or alter external stimuli to the patient.  This may include decreased hearing or unfamiliar sounds, or changes in the visual environment.

One of the most common times for delirium to occur is in the evening (so-called “sundowning” (see above picture)). Patients may become highly agitated, active, confused, combative, anxious and/or restless in the late afternoon or evening. This behavior can be quite out of the ordinary and be very difficult to manage for the family and medical staff.  Sundowning commonly occurs in elderly hospitalized patients, who are out of their normal environment, sleep-deprived, often in pain, post-surgery, and/or under the influence of sedatives or analgesics.

In summary, differentiating between delirium and dementia can be challenging. It is very important to talk with family to obtain a careful background history on the patient to see if they have underlying cognitive problems. Furthermore, a patient that starts out the hospital course relatively intact, then develops symptoms acutely later on almost certainly has delirium rather than dementia. A fluctuating course suggests delirium rather than dementia. Poor attention suggests delirium. The hallmark for differentiating between the two is the state of consciousness. Alteration of consciousness suggests delirium, as patients with dementia usually have an intact level of consciousness..

Features Useful in Differentiating Delirium from Dementia