Delirium, Dementia, and Amnesia in Emergency Medicine 

Delirium, dementia, amnesia, and certain other alterations in cognition are subsumed under more general terms such as mental status change (MSC), acute confusional state (ACS), or organic brain syndrome (OBS). Acute alterations in brain function are commonly referred to as MSC or ACS; chronic alterations and any MSC specifically due to nonpsychiatric causes are typically included in the organic brain syndrome category.

Although the term organic brain syndrome is used to distinguish changes in cognitive/behavioral functions due to physical (organic) causes from those due to psychiatric (functional) causes, there has been a growing recognition of the organic bases of many psychiatric disorders. Therefore, the distinction between organic and functional has become blurred. As a result, the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), no longer recognizes organic brain syndrome as a diagnostic entity.

However, in practice, organic brain syndrome is conceptually useful to the practicing emergency physician by highlighting a sizable list of diagnoses to be considered before a patient with abnormal mentation and/or behavior is presumed to solely have a psychiatric illness. If a more precise diagnosis of a change in mental status can be determined, the nebulous term organic brain syndrome should be abandoned.

Organic brain syndrome can be divided into 2 major subgroups: acute (delirium or acute confusional state) and chronic (dementia). A third entity, encephalopathy (subacute organic brain syndrome), denotes a gray zone between delirium and dementia; its early course may fluctuate, but it is often persistent and progressive.

The final common pathway of all forms of organic brain syndrome is an alteration in cortical brain function. This condition results from (1) an exogenous insult or an intrinsic process that affects cerebral neurochemical functioning or (2) physical or structural damage to the cortex. Some of the etiologies include trauma, mass lesions, hydrocephalus, strokes (ie, multi-infarct dementia), atrophy, infection, toxins or dementing processes.

The end result of these disruptions of function or structure is impairment of cognition that affects some or all of the following: alertness, orientation, emotion, behavior, memory, perception, language, praxis, problem solving, judgment, and psychomotor activity. Knowledge of which areas of this spectrum are affected or spared guides both the workup and the diagnosis.

Frequency

United States

Delirium accounts for 10-15% of admissions to acute-care hospitals (but is usually not the primary diagnosis).

The prevalence of dementia doubles every 5 years between ages 60 to about 90: 1% of persons aged 60-64 years up to 30-50% of those older than 85 years. Approximately 60% of nursing home beds are occupied by patients with dementia. In the ED, patients in nursing homes are more likely to present with delirium than other patients, even after adjusting for delirium risk factors.^[1] Alzheimer disease (AD) accounts for most patients with dementia who are older than 55 years (50-90% of all cases).

Although slowing of memory and word-finding are a normal feature of brain aging, approximately 50% of patients with mild cognitive impairment whose day-to-day functioning is as yet unaffected develop the onset of dementia within 3 years. Various risk-stratification tools have been developed over recent years to aid in both lifestyle counseling and dementia research.

International

Alzheimer disease is less common and has an older age of onset in Japan, China, and parts of Scandinavia. In these countries, vascular causes of dementia may outnumber Alzheimer disease.

Mortality/Morbidity

Some causes of delirium (eg, delirium tremens, severe hypoglycemia, CNS infection, heatstroke, thyroid storm) may be fatal or result in severe morbidity if unrecognized and untreated. With some exceptions, such as overdose of tricyclic antidepressants, drug intoxications generally resolve fully with supportive care. Failure to provide thiamine when administering glucose may rarely lead to acute Wernicke syndrome (ataxia, confusion, oculomotor palsies in the setting of malnutrition). If unrecognized, Wernicke syndrome may also result in chronic organic brain syndrome.

Certain withdrawal syndromes (eg, alcohol, benzodiazepines, barbiturates) can be deadly if untreated.

Patients with primary dementia have a significantly reduced life expectancy, depending on the cause of the dementia and its severity and rapidity of progression.^[2]

Race

Delirium is seen more commonly in whites than in other races.

Sex

Delirium is seen more commonly in females than in males. Alzheimer disease is more prevalent among women because of their longer life expectancy. Lifetime risk in women is estimated to be 32%, whereas the lifetime risk in men is 18%. However, the age-specific risk is equal in both sexes.

Age

Delirium due to physical illness is more frequent among the very young and those older than 60 years. Delirium due to drug and alcohol intoxication or withdrawal is most frequent in persons aged mid teens to the late 30s.

Dementia, particularly Alzheimer disease, is seen predominantly in elderly persons; however, certain types of dementia are seen in younger patients (eg, AIDS-related dementia, certain familial forms of Alzheimer disease), and some cases of variant Creutzfeldt-Jakob disease (ie, bovine spongiform encephalopathy or mad cow disease). AIDS-related dementia is the most common nontraumatic dementia seen in younger persons.