Dementia

Aetiology

It is clinically essential to establish the underlying aetiology of dementia as the syndrome will be reversible in some cases and may be arrested or progression delayed in others. The main causes of the dementia syndrome are listed below.

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Depression

Major depressive disorder may include significant memory impairment, together with difficulty in thinking and concentrating, and an overall reduction in intellectual performance. A mild dementia syndrome can be difficult to differentiate from depressive pseudodementia. Establishing the premorbid state of the individual, when and how the disorder started, and the course of the depressive and cognitive symptoms may help to clarify the aetiology of the disorder.

Depressive Pseudodementia

Some differences between true dementia and depressive pseudodementia are outlined here.

Delirium

Delirium is an acute confusional state with relatively abrupt onset and is generally readily distinguished from dementia. However it be an early sign of impending dementia and may co-exist with dementia, in this situation both conditions should be diagnosed.

Delirium differs from dementia because delirious patients have a markedly reduced ability to maintain and shift their attention properly and have fluctuating symptoms. This is in contrast to the relatively stable symptoms of dementia. In addition, episodes of delirium are generally brief – days or weeks, rarely more than a month.

Some characteristic differences between delirium and dementia are outlined in the table below.

Danish College of General Practitioners - how to differentiate dementia, delirium and depression.

The differences between dementia and depression, as defined by the DSM-IV, are outlined below.

Reversible Causes

Substance Abuse

This is predominantly abuse of alcohol, however, some 'recreational' drugs and exposure to toxins and heavy metals may lead to dementia, delirium or both. A thorough clinical and social history, especially with the aid of a reliable informant, together with the psysical examination will serve to discriminate these problems.

Whilst abstinence will largely reverse the problem in most cases of substance abuse, toxins and heavy metals may lead to irreparable neurological damage associated with a true dementia syndrome. Moreover, consideration must be given to the possibility that substance abuse is overlaid on dementia, so investigation of aetiology should not stop the point.

Medications

Some medications, e.g. sedatives, hypnotics or medicines with cholinergic side effects, may lead to a memory loss or other cognitive problems. Their discontinuation will lead to restoration of normal function when dementia is not also present.

However, other possible causes of dementia need to be investigagted even if a person has substance dependence, or has been exposed to toxins.

Some potentially reversible causes of the dementia syndrome
Hypthyroidism	May lead to a demetia syndrome
Hypercalcaemia	May mimic dementia
Hypoglycaemia	May be asociated with confusion and symptoms similar to dementia
Nutritional deficiencies	May be associated with the dementia syndrome
Kidney and liver disorders	Dysfunction, often secondary in the liver disease to alcohol abuse, may lead to the dementia syndrome (90% of alcoholics develop dementia)
Infections	Chronic infections may be associated with a dementia-like condition. Conditions such as borrelioses, neurosyphilis and HIV can lead to dementia and should be considered when the patient's lifestyle or history indicates risk. AIDS-related dementia is probably a direct consequence of HIV infecting the central nervous system (CNS)
Normal pressure hydroephalus	This is a brain disorder caused by blockage of the flow of the CSF. It leads to enlargement of the ventricles and compression of brain tissue. As a result brain atrophy and dementia can occur. Structural brain imaging techniques such as CT scannning can establish whether this disease has caused the dementia

Differentiation of the Dementias

In the majority of cases where a dementia syndrome is established, a neurologically degenerative disorder will be the underlying cause. However, as this is such a condemning diagnosis at the present state of therapy, it is essential that all potentially reversible causes should be fully investigated.

Whilst Alzheimer's disease (AD) is the predominant aetiology of the dementias, differential diagnosis is often complicated by the fact that features of other types of dementia, such as Vascular dementia (VaD) or Lewy body dementia (LBD) are also present as, shown in the diagram below.

Diseases causing dementia – mixed disorders

Taken from figure 8, page 31, Early Diagnosis and Treatment of Alzheimer’s Disease by Simon Lovestone (supported by Novartis)

Several scientific societies and consensus groups have produced criteria and guidelines for the diagnosis and treatment of dementia/AD. However, medical traditions for investigating dementia vary from country to country and between the medical specialities. The need for and value of EEG, lumbar puncture and even brain scans remain subjects of debate. Some physicians, usually neurologists, recommend hospital admission for investigation; whereas other physicians, mainly psychiatrists, recommend carrying out most of the investigation in the patient’s own home.

For all involved in the detection and differentiation of the dementias, it will be necessary to be thoroughly aware of both international and local good practice and guidelines. One of the more common general definitions for diagnosis of AD is that of the National Institute of Neurological and Communicative Disorders and Stroke – Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA). The NINCDS-ADRDA makes it clear that a definite diagnosis of AD can only be made using pathological examination of the brain and pre-mortem diagnosis of AD is very unlikely.

NINCDS-ADRDA criteria for Alzheimer's disease (McKhann et al 1984)
Possible AD	Dementia with variations in onset or course. Presence of systemic or other brain disorder. Single progressive cognitive deficit.
Probable AD	Dementia by history and neuropsychological testing. Progressive deficits in memory and one other area of cognition. No disturbance of consciousness. Onset between age 40 and 90 years. Absence of systemic or other brain disorder causing dementia.
Definit AD	Clinical criteria for probable AD. Histopathology of AD by biopsy and autopsy.

Considering that a mixed aetiology is not uncommon in dementia, a diagnosis adequate for clinical management may be established in many cases on the basis of clinical signs and symptoms. A comparison of the major types of dementia is outlined below.

The course of the disease process will also give significant clues to the underlying aetiology. A diagrammatic representation is shown below.

DSM-IV Criteria for Alzheimer’s disease

DSM-IV codes for dementhia of the Alzheimer type

Code based on type of onset and predominant features. With early onset: if onset is at age 65 years or below 290.11 With delirium: if delirium is superimposed on the dementia 290.12 With delusions: if delusions are the predominant feature 290.13 With depressed mood: if depressed mood (including presentations that meet full symptom criteria for a major depressive episode) is the predominant feature. A separate diagnosis of mood disorder due to a general medical condition is not given 290.10 Uncomplicated: if none of the above predominates in the current clinical presentation

With late onset: if onset is after age 65 years 290.3 With delirium: if delirium is superimposed on the dementia 290.20 With delusions: if delusions are the predominant feature 290.21 With depressed mood: if depressed mood (including presentations that meet full symptom criteria for major depressive episode) is the predominant feature. A separate diagnosis of mood disorder due to a general medical condition is not given 290.0 Uncomplicated: if none of the above predominates in the current clinical presentation

Specify if: With behavioural disturbance