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Alzheimer's - Detection
and diagnosis
The onset of Alzheimer's is often so gradual and the early
signs so benign (forgetfulness, getting a bit muddled up,
decreased interest in hobbies, food, etc.) that they can easily
be mistaken for normal mental ageing. It is important to separate
these two, because the treatments now available are most useful
in the early stages and can often delay the development of
more serious symptoms, at least for a time. So if these traits
are becoming a concern to the family, it is important to persuade
the individual to go and see their doctor, who may refer them
for more detailed examination by a specialist.
Unfortunately, there is no simple blood or urine test that
can detect Alzheimer's and diagnosis will depend largely on
two strategies:
- the elimination of other possible causes of the symptoms
(quite a few causes, such as depression, can be very adequately
treated) and
- a careful assessment of the family and personal history
of the individual and their symptoms. From this kind of
information, Alzheimer's and vascular dementia can be distinguished,
because their basic characteristics are quite different.
The elimination of other causes can often be done simply
by sending blood and/or urine samples for analysis, and from
a direct clinical examination. The test results may take a
week or two to come back, but if they fail to suggest a cause,
it is likely that the individual will be given further simple
tests, often by a psychiatric nurse. This is called an assessment.
Examples would be:
- a test for the recall of items from a list of common objects
read out to them, called 'word list learning tests'. Recall
might be checked immediately after reading, after ten minutes
or even longer
- recognition of pictures of well-known people
- naming of common objects from pictures would test the
person's ability to associate words with images correctly
- asking simple questions such as 'What is the name of the
Prime Minister?' or 'What are the names of your four grandchildren?'
- simple maze drawing tests.
| FEATURE |
ALZHEIMER’S |
VASCULAR DEMENTIA |
|
|
| Age of onset |
Usually after 65 |
Usually after 40 |
| Sex |
Commoner in women |
Commoner in men |
| Course |
Gradually progressive |
‘Step ladder’ |
Impaired insight,
intelligence and personality |
Early |
Late |
|
Physical signs
and symptoms
|
Usually few and appearing late in
the illness
|
Usually present and of sudden onset
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It has been shown that word learning and recall and some
maze tests are impaired even in early Alzheimer's. Hence,
based on experience with many people, the assessor will probably
have some idea from the results obtained as to whether the
symptoms are merely normal ageing or something more serious.
They will often want to repeat the tests after a few weeks
or months to see if there has been any change.
The doctor or nurse will also want detailed information on
other members of the family who have had dementia, and also
details of how the symptoms have developed in the person being
examined. Armed with all this information, an experienced
practitioner will be able to diagnose Alzheimer's with 80
to 90 per cent certainty.
Brain scans such as Computed Tomography (CT), Magnetic Resonance
Imaging (MRI) and Positron Emission Tomography (PET) can be
used to confirm diagnosis, but in the very early stages they
often fail to show very much change. Later on, there will
be a significant and clear loss of brain tissue and an enlargement
of the fluid-filled spaces (ventricles) in the brain, but
by then the diagnosis is probably fairly certain. Scans are
most likely to be performed in early-onset cases or to eliminate
other causes, for example, if a brain tumour is suspected.
Unfortunately, the definitive signs of Alzheimer's, namely
the presence of amyloid plaques and neurofibrillary tangles,
can only be seen after death, when brain tissue can be examined.
These features are present in tissue removed from a living
brain (a biopsy), but taking biopsies is too risky to be widely
practised unless there is some other good reason for doing
so.
The diagnosis of Alzheimer's would be greatly helped if easily
measured biochemical markers of the illness could be found.
The tau protein found in neurofibrillary tangles can be used
as a diagnostic marker, but unfortunately, it is only found
in the cerebrospinal fluid, whose collection requires a lumbar
puncture. Recently, however, a compound called isoprostane
has been shown to rise dramatically in the urine of both people
with Alzheimer's and Down's syndrome. This compound is a product
of damage to fat molecules by very reactive forms of oxygen
called Reactive Oxygen Metabolites, or ROMs. Levels of isoprostane
correlated directly with tau protein and beta-amyloid. If
this observation is confirmed, it could lead to a simple diagnostic
test in the near future.
Finally, readers may encounter references in the literature
to special tests for a variety of aspects of mental function
in Alzheimer's. A common one is called the Alzheimer's Disease
Assessment Scale, usually written as ADAS. Varieties of this
scale deal with, for example, cognitive performance, when
the abbreviation is ADAS-COG. Others are CIBIC, which stands
for Clinician Interview-Based Impression of Change, and CDR,
which is the Clinicians Dementia Rating scale. These scales,
and others like them, are often used by specialists or in
clinical trials of new medicines, where there is a need to
measure any decline or improvement as accurately as possible.
Only by such techniques can the effect of any new treatment
be convincingly measured.
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