Dementia

The prevalence of dementia in Australia and most developed nations is approximately 6.5% among people aged 65 years and over. The prevalence rises exponentially with age, doubling every 5 years after the age of 65 years. The incidence of dementia (the number of new cases per year) also rises exponentially with age, with a similar doubling every 5 years.

Amnestic disorder

Although the true prevalence of amnestic disorder is not reliably known, an Australian autopsy series found signs of the Wernicke-Korsakoff syndrome in 2.8% of brains, the highest prevalence ever reported (for a review see Harper et al 1995). However, more recent research has suggested that the fortification of flour with thiamine might have reduced the prevalence of this condition (Harper et al 1998). The syndrome of amnestic disorder is sometimes considered to be a subtype of dementia, although by definition it is not associated with the global cognitive impairment associated with dementing illnesses.

Delirium

Delirium is also known as acute confusion or acute brain syndrome, and these terms highlight the acute nature of the condition. The community prevalence of delirium is not reliably known, but it is present in 15–35% of older hospital inpatients, either on admission or within 3 days of admission.

Dementia

The cardinal feature of dementia is decline from a previous level of cognitive performance involving memory and at least one of the following: aphasia, apraxia, agnosia and executive dysfunction. Aphasia is a language and communication disorder; apraxia is an abnormality of complex movement despite normal peripheral motor function; and agnosia is an inability to recognise objects despite normal sensory function. Executive dysfunction involves abnormalities in planning, organisation, initiation and checking of behaviour. In most cases of dementia, there is progressive and irreversible deterioration in cognitive function. However, some cases of dementia are caused by acute insults to the brain, such as head injury or encephalitis. In such cases, there may be the prospect of some improvement in cognitive function over several months following the acute event.

Amnestic disorder

In amnestic disorder, clinical impairment is restricted to memory function, rather than the global cognitive impairment found in dementia. People with amnestic disorder have particular difficulty with new learning, while other cognitive functions remain relatively intact. In severe cases of amnestic disorder, the person is completely unable to make new memories and remains like this permanently.

Delirium

Delirium is characterised by the acute onset of global cognitive impairment, fluctuating clouding of consciousness, altered day/night cycle, psychomotor agitation (one-third of People) or psychomotor retardation (two-thirds of People). Delirium is considered a neuropsychiatric emergency because quick action may prevent a poor outcome for the person and may even prevent death. Delirium is a clinical chameleon and can mimic other conditions, such as dementia, psychosis, anxiety, depression and mania.

Dementia

Most cases of dementia are caused by Alzheimer’s disease or cerebrovascular disease, or a combination of the two (so-called mixed dementia). However, there are more than 70 other diseases that cause dementia, including frontotemporal lobar degeneration (FTLD), dementia with Lewy bodies (DLB), alcohol-related dementia, Parkinson’s disease, traumatic brain injury (TBI), normal pressure hydrocephalus (NPH), hypoxic encephalopathy, Huntington’s disease, herpes simplex encephalitis and Creutzfeldt-Jakob disease (CJD).

Alzheimer’s disease is associated with progressive brain atrophy. Microscopic examination of the brain in this condition reveals neuronal loss, accumulation of extracellular neuritic plaques and intracellular neurofibrillary tangles, and a variety of other neuropathological features. In addition, there is massive loss of synapses, particularly acetylcholine synapses. Although the underlying aetiology of Alzheimer’s disease is still being studied, the common late-onset sporadic form of the disease appears to be caused by a combination of advancing age, susceptibility genes such as the gene for apolipoprotein E, and environmental factors. Putative environmental factors include reduced brain reserve due to poor education and lack of cognitively stimulating activities.

Various types of cerebrovascular disease are associated with dementia, including multiple infarcts (strokes), subcortical damage to cerebral white matter (deep white matter ischaemic changes), hypoxic encephalopathy, small strokes in strategic locations (e.g. the thalamus), and several rare inherited vascular syndromes, including CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy).

Amnestic disorder

There are many different causes of amnestic disorder, although only one common cause in the developed world—thiamine (vitamin B1) deficiency, which is often associated with alcohol dependency. Recent research indicates that the characteristic brain changes of this focal syndrome may also be present in alcohol-dependent people who present clinically with more generalised dementia. The Wernicke-Korsakoff syndrome is at least partially reversible in many People once thiamine replacement has been implemented and alcohol intake has ceased. Uncommon causes of thiamine deficiency include bulimia nervosa, hyperemesis gravidarum (excessive vomiting during pregnancy) and chronic gastrointestinal disease. Rare causes of amnestic disorder include carbon monoxide poisoning and herpes simplex encephalitis.

Delirium

Delirium may be caused by any acute medical problem that either primarily or secondarily affects the brain. Common causes in older people include intercurrent infections, organ failure, metabolic disease, prescribed medication and alcohol withdrawal. Other common causes include stroke, acute myocardial infarction and cancer. Common intercurrent infections include those of the urinary tract, lungs and skin. Organ failure includes cardiac failure, respiratory failure, renal failure and hepatic failure. Metabolic disease includes diabetes mellitus. Drugs with powerful anticholinergic effects, such as older-style antidepressants (tricyclics), antipsychotics, antiparkinsonian agents and drugs to treat urinary incontinence, are particularly likely to precipitate delirium in older people otherwise predisposed to this condition

Dementia

Differential diagnoses include:

Amnestic disorder

Differential diagnoses include:

Delirium

Differential diagnoses include:

History overview

It is important to obtain a reliable history if one of these three cognitive disorders is suspected. This history should be obtained from an informant who has regular contact with the older person. It would be unsafe to conclude that an older person was not suffering from one of these three conditions without speaking with an informant.

The critical distinction between dementia and delirium is in the history of onset. Most cases of dementia have a slow and insidious onset, whereas most cases of delirium have a rapid onset (over hours or days). Textbooks often describe a ‘stepwise’ deterioration in cases of multi-infarct dementia, but most cases of vascular dementia do not have this history. The course of onset of amnestic disorder is more varied.

Dementia of recent onset or rapidly progressive dementia raise additional issues. Such dementias may be due to remediable causes, such as severe depression or subdural haematoma, or due to unusual causes, such as cerebral vasculitis or CJD. As a general principle, People with dementia of recent onset (weeks to a few months) should be referred urgently for neurological review.

The person with delirium exhibits fluctuations in their level of consciousness and in the expression of their other symptoms. They may have lucid intervals in which they seem normal. In contrast, the person with dementia usually exhibits a much more stable state of mind. However, there are some exceptions to these general rules. The first is that dementia and delirium can coexist; the second is that many people with dementia exhibit so-called ‘sundowning’ (late afternoon deterioration) and alterations in their sleep continuity; and the third is that many People with DLB show brief alterations in their level of consciousness.

Amnestic disorder is suspected when the person presents with acquired memory impairment in the absence of global cognitive decline. There is usually dense anterograde amnesia as well as retrograde amnesia. Confabulation often occurs in amnestic disorders.

History: specific types of dementia

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Consumers and carers Clinical cognitive assessment Functional assessment Community management of acutely ill older people Psychosocial and spiritual assessment Prevention and promotion

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