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Common forms of dementia

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VOL: 98, ISSUE: 46, PAGE NO: 32

Graham A. Jackson, MB, ChB, MRCPsych, MRCGP, is consultant old age psychiatrist, Leverndale Hospital, Glasgow

PART 1 of this four-part series looked at the common features and prevalence of dementia and at one of the most common forms - Alzheimer's disease. This part continues by looking at further forms of dementia and how they can be recognised.

PART 1 of this four-part series looked at the common features and prevalence of dementia and at one of the most common forms - Alzheimer's disease. This part continues by looking at further forms of dementia and how they can be recognised.

Vascular dementia
This term is more inclusive than the older 'multi-infarct dementia', and takes into account the fact that the presence of infarcts is by no means essential for the development of dementia. Indeed, even in the presence of brain damage demonstrated by scanning techniques, there is only a vague correlation between the amount of tissue affected and the degree of cognitive impairment.

Vascular dementia tends to be of more sudden onset than Alzheimer's, and progression is usually in a step-wise manner: sudden episodes of decline, with plateaux, which may sometimes be very long, in between. Vascular disease is only rarely confined to the brain, so patients usually have other vascular problems, or at least the presence of one or more risk factors. There is often a history of strokes or of transient ischaemic attacks, or a history of hypertension, smoking, angina or diabetes.

Cognitive impairment may be patchy, depending on where damage has occurred. Rather than specific infarcts, as the term multi-infarct might suggest, more often there are generalised ischaemic changes in the white matter throughout the brain.

As yet, there are no specific treatments for vascular dementia. It is obviously important to try to recognise and manage the vascular risk factors. Apart from those already mentioned, these include being overweight, poor diet, and abnormal lipid profiles. Although treatment with low dose aspirin has been shown to help prevent stroke or myocardial infarction in those at risk, there is no evidence of benefit in the prevention or treatment of vascular dementia (Williams et al, 2002).

Genetic factors are less prominent in vascular dementia than they are in Alzheimer's other than in relation to the risk in generalised vascular disease. There is a rare form of vascular dementia that affects a younger patient group (usually in their mid-40s) and which results in the development of dementia, transient ischaemic attacks and stroke. This is called cerebral autosomal dominant arteriopathy with subcortical infarcts and leuco-encephalopathy syndrome, or CADASIL. The gene for this has been identified on chromosome 19.

A diagnosis of probable vascular dementia is made on the basis of a dementia that is of sudden onset, of stepwise progression, and shows evidence of focal neurological signs (or focal cognitive deficits), with evidence of other vascular problems such as hypertension. Of course, Alzheimer's and vascular dementia can co-exist - a mixed dementia - and indeed there are suggestions that Alzheimer's may have a microvascular origin.

Frontotemporal dementia
This term is now thought to be more appropriate than the terms 'frontal lobe dementia' and 'Pick's disease'. Arnold Pick first described the clinical syndrome of progressive personality change associated with bilateral frontal lobe atrophy in 1906.

Like Alzheimer's, frontotemporal dementia appears to be a syndrome that may result from various different causes. The common pathological picture is one of severe atrophy in the frontal and anterior temporal region, which is usually, but not always, symmetrical. In some cases, typical Pick bodies are seen - protein (tau and ubiquitin) inclusions within neurones (Fig 1). Their significance is unclear.

Frontotemporal dementia tends to affect a younger age group than does Alzheimer's or vascular dementia, is more common in women than men, and has a stronger genetic component. Onset is insidious, with personality change and prominent dysphasia rather than memory impairment. Difficulties with memory often appear at a late stage, although communication problems can make it appear much worse than it actually is. Its clinical features were detailed in Part 1 in the description of the frontal lobe. Primitive reflexes may be present, particularly the sucking or pout reflex.

Dementia with Lewy bodies

This appears to be a separate form of dementia, although some authorities see it as a variant of Alzheimer's.

Lewy bodies are small inclusions in cells, comprised of insoluble complexes of proteins totally different to the tangles of Alzheimer's (Fig 2). The inclusions have long been recognised in the basal ganglia of the brain in patients with Parkinson's disease. It is, however, only in the past 15 years that they have been identified in the cortex of patients with this form of dementia. The main features of dementia with Lewy bodies are shown in Box 1.

Of particular diagnostic (and clinical) importance is the fluctuating nature of the cognitive impairment, the presence of often very vivid visual hallucinations, and sensitivity to neuroleptic drugs. These drugs are often used first-line in the management of hallucinations in other contexts, so the possibility of dementia with Lewy bodies must always be considered in such patients. The newer so-called atypical neuroleptic drugs are safer, although patients are often able to tolerate only small doses.

Huntington's disease
This is an autosomal dominant condition, which means that 50 per cent of the children of patients with the condition will be affected. Thus there is virtually always a family history. Age of onset varies from the late teens to the 70s, although it is most common in the 30s. As well as dementia there is a particular movement disorder (chorea), and often psychiatric problems such as paranoia or depression. In fact, the latter may be the first signs of the illness.

The genetic abnormality has been identified as being on chromosome 4, with an abnormal number of repeats of a particular protein grouping. Genetic screening is now available, including prenatal screening. Obviously this gives rise to various ethical issues, including informed consent, possible termination of pregnancy, and disclosure to others.

Normal pressure hydrocephalus
This is fairly uncommon. It is particularly important to recognise it, as it may be possible to treat it surgically. It is caused by an interference with the flow of cerebrospinal fluid around the brain, and can be a late result of previous brain disease such as subarachnoid haemorrhage, or meningitis. The pressure changes in the ventricles of the brain cause damage to surrounding structures, resulting in a particular triad of symptoms - memory impairment, urinary incontinence and gait disturbance. Following a suspicious scan, pressure studies can be carried out by a neurosurgeon and, if the investigations prove suitable, a shunt can be inserted to drain excess fluid from the brain. Results of such surgery are variable, but may prevent further deterioration.

Secondary dementias
Dementia may be associated with other conditions such as Parkinson's disease, stroke and various forms of cancer (particularly of the lung). Deficiencies of folic acid, thyroid hormone and of vitamin B12 have all been implicated in causing dementia but treatment is usually disappointing in terms of improving cognitive function.

Cognitive impairment can be caused by excess alcohol, but there may be a particular form of dementia that is associated with drinking too much (alcohol-related dementia) although, more commonly, memory problems result from a condition known as Korsakoff's psychosis. The impairment results from a deficiency of the vitamin thiamine, a consequence of poor dietary intake, and from alcohol interfering with the vitamin's metabolism. (There are causes of Korsakoff's psychosis other than alcohol, including malnutrition and severe vomiting in pregnancy, but these are rarely severe enough to cause the condition.) Memory impairment is often severe, typically with particular damage to short-term memory and disorientation in time, with relative preservation of other cognitive abilities and social skills.

Pathologically, the main finding in patients with Korsakoff's psychosis is atrophy of the mamillary bodies in the base of the brain. Strictly speaking, it is not a true dementia because after cessation of drinking there is no further deterioration, and it can improve up to a point (often over several months), so decisions on long-term care should not be taken prematurely.

There is a form of dementia related to HIV infection. Early worries of an epidemic of AIDS-related dementia have not, however, materialised. The dementia tends to occur in late-stage illness, where cognitive impairment is less of an issue than often very severe physical problems.

Much has been written recently about Creutzfeldt-Jakob disease (CJD). It is not a new disease, the name having been coined in 1922. It was thought then to be a disease affecting older people. It is rare, and is associated with physical deterioration as well as a rapidly progressive dementia. Recent discussion around the illness refers to new variant CJD, which affects younger people and is almost certainly related to bovine spongiform encephalopathy (BSE) in cows (Fig 3). Although CJD is sometimes inherited in an autosomal dominant fashion, in many cases, and probably in all new variant cases, it is transmitted by proteins called prions, which have the ability to mutate, causing the death of brain cells.

Consequences of dementia
By the time dementia is diagnosed it is likely that the person will have suffered various physical and cognitive losses, some as a result of getting older, some because of growing frailer and some because of the dementia itself. There is also often loss of role, including perhaps that of occupation, or of being a householder, and perhaps loss of a spouse. Cognitive impairment might possibly have resulted in loss of decision-making abilities, of self-care skills, of memory and perhaps even of dignity.

Memory is not an all-or-nothing thing: it may fluctuate, and it may affect different aspects of remembering. In the early stages of Alzheimer's, mainly short-term memory is affected. The effect of this is, for example, forgetting to eat or to go to bed, or perhaps telephoning someone six times in half an hour. Continuing to live at home becomes increasingly difficult as daily living abilities decline. To be able to dress unaided, prepare and eat food, and toilet are essential skills if one is to look after oneself.

Summary
This part has looked at some of the common forms of dementia (Box 2), indicating the signs and symptoms so that appropriate identification can be made and the most suitable type of treatment can be instigated.

Next week: Behavioural problems and assessment

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