dementia

dementia …Last scene of all,
That ends this strange eventful history,
Is second childishness, and mere oblivion,
Sans teeth, sans eyes, sans taste, sans everything
[ Shakespeare , As You Like It]


We all fear disintegration of the mind, and rightly so; it robs us of our dignity. Bereft of reason we cannot contribute to society, vote, write a will, nor with time care for our basic needs. The disintegration of the mind, or dementia, is a familiar occurrence in the elderly but can occur at any age and result from a vast array of diseases. The loss of acquired intellectual skills — the characteristic feature of dementia — is distinct from developmental failure, which results in learning difficulties of variable severity. We may also be robbed of our senses by sleep or inebriation, and so the term ‘dementia’ is restricted to individuals who are awake and alert. Similarly, patients with a restricted cognitive deficit such as impairment of language following a stroke may have a very different prognosis, with preservation of other intellectual functions, when compared with the widespread disintegration commonly seen with the dementing diseases. A definition of dementia has thus emerged to describe an individual who is alert but who suffers impairment in more than one cognitive domain, of sufficient severity to impair social function. A difficulty in applying the definition is to decide what is a specific cognitive domain. Impairment of memory is considered essential, or more specifically impairment of event memory: that which allows us to recall day-to-day events and maintains our sense of continuity; impairment of memory is a salient feature of Alzheimer's disease, the commonest cause of dementia. Other cognitive domains may include language; visuospatial and visuoperceptual functions, which allow interpretation of our visual world; and so-called ‘frontal executive skills’, which allow us to plan and select appropriate responses to our environment.

It is important to emphasize that dementia is a syndrome and not a disease. The challenge to the clinician is to identify the underlying cause, of which there are many. Alzheimer's disease is the commonest, particularly in the elderly; it is thus the main cause of ‘senile dementia’, a term that is becoming obsolete. It was described in 1906 by Alois Alzheimer, and was considered a rarity occurring in relatively young people (‘pre-senile dementia’), until the 1960s, when it was recognized that the microscopic abnormalities described by Alzheimer were also found in the demented elderly. This led to an apparent epidemic as patients were reassigned from the categories of ‘just old age’ or ‘senile dementia’ to Alzheimer's disease.

Alzheimer had exploited the newly-discovered silver staining method for microscopic examination of nerve tissue, to visualize abnormal cellular changes in the brain. He studied the brain of a 51-year-old patient, Auguste D., whom he had seen whilst working in Frankfurt and who died at the age of 54 years with severe dementia. He reported the hallmark features: ‘neurofibrillary tangles’ and ‘senile plaques’. Recent research has shown that the neurofibrillary tangle results from a collapse of the ‘internal skeleton’ of brain cells (the neuronal cytoskeleton). Senile plaques consist of disrupted neuronal connections, axons, and dendrites, around a core of abnormal deposits of a protein called beta amyloid. This protein undergoes a change in shape that renders it harmful to the cell; exactly how and why these changes occur is the subject of intense research aimed at finding effective treatments.

Alzheimer's disease is the prototypic dementia, characteristically starting with mild forgetfulness and a tendency to repetition in conversation: memory failure worsens, with appointments and recent events forgotten. Losing their way, at first in unfamiliar and then in familiar surroundings, patients become increasingly bemused and testy. Failure of language follows, with increasing difficulty in making sense of the world around them. Dressing, feeding, and toiletting all require help before the final stage ‘sans everything’.

A variety of other degenerative diseases have been, and are being, identified as causes of dementia, including Creutzfeldt Jakob disease and Pick's disease. The latter was described as long ago as 1894. Arnold Pick, a neurologist from Prague, reported a patient with loss of language who was found to have circumscribed shrinkage or atrophy of the temporal lobe, the area of the brain involved with language function. Pick reported the case to disprove the prevailing dogma that all senile atrophies inevitably involved the whole brain. It was Alzheimer's subsequent analysis of such cases that identified silver-stained ‘Pick bodies’ as distinct from the neurofibrillary tangles of his own eponymous disease. Pick's disease is rare and cannot be reliably diagnosed without examination of brain tissue after death, and so is generally swept up in the wider diagnostic category of the fronto-temporal degenerations. Reflecting the areas of the brain affected, such patients present with impairment of language or of social behaviour; whilst at first the symptoms may be confined to one cognitive domain, other functions decline and the clinical picture becomes that of a dementia.

Before the demonstration that the changes of Alzheimer's disease were the common accompaniment of dementia in old age, it used to be thought that such cases were due to a failure of the blood supply, starving the brain of oxygen. There is no evidence that this is so, but multiple strokes can result in dementia, as can multiple haemorrhages into the brain. These are subsumed within the broad category of vascular dementia, which represents the second commonest cause of cognitive impairment, according to some reports.

The ‘use it or lose it’ school of thought argues that education may in part protect us from Alzheimer's disease. But no one is exempt. Scholars, scientists, artists, and statesmen have all succumbed. The publicity surrounding Ronald Reagan's diagnosis of Alzheimer's disease has done much to focus research funding, whereas the same diagnosis in Finland's President may have affected his ability to govern in the last few years of office in the early 1980s.

A small minority of dementias are eminently treatable, and vascular dementia is anticipated to become less common with better management of risk factors such as heart disease, hypertension, and smoking. The major challenge is Alzheimer's disease, and the challenge is a global one, with a predicted 34 million affected individuals by the year 2025. Most will be in the emerging nations, where life expectancy is increasing. In China this is combined with a policy of one child per family, such that the future work force will have to provide for a disproportionate dependent population; the solution will owe as much to politics as to medicine.

The conceptual shift in our understanding of dementia has been profound; no longer is it seen as an inevitable concomitant of old age. Instead we can view Alzheimer's disease, the major cause of late life dementia, as a disease with distinct physical changes, which should be amenable to treatment. However, we should not confuse this with the inevitable changes of ageing. We cannot run as fast at 90 as at 20, nor can we think as fast. We can, though, anticipate the preservation of wisdom and knowledge; to exploit the latter is a challenge for society, to preserve them and avoid dementia is a challenge for medicine.

Martin Rossor

See also ageing; memory; psychological disorders; senility.