The following diagram presents an outline of the diagnostic process for dementia. Many of the elements are discussed in greater depth in aetiology of dementia.
Initial Assessment of Memory and Function
A worrying tendency to forget recent events, appointments, bills and other things that need attention often motivates the patient or care-giving relation to seek for a medical opinion.
The patient’s or carer’s worries can usually be assessed without recourse to formal testing procedures, especially if a reliable informant is present during the evaluation and/or the physician is familiar with the patient’s clinical history and general situation.
Assessment of the problem generally begins with a patient interview to establish the present level of cognitive functioning and the extent of change from prior functioning. The interview is preferably conducted in the presence of a partner, close relative or another reliable informant. This preliminary interview will generally assess the present levels of memory, language ability and executive function. Impaired memory may be evident in how the patient responds to quite simple questions; in searching for words to express him or herself; or in direct complaints. For example, individuals with impaired memory may not recall recent events, forget that food is cooking or misplace items such as keys, spectacles or money.
When the patient answers questions, it is important to note whether the ‘head turning sign’ is present. A person with cognitive impairment will often turn their head to their spouse/caregiver to have them provide answers. This person is often critical in the assessment, as patients may lack insight and their responses will often require verification. Perhaps more importantly, the observer may give a more reliable assessment of changes in functional abilities.
In addition to a patient’s clinical and social history other questions might be used in this initial assessment and these are outlined in the table below
Physicians have recognise that there is a general age-related decline in memory and make appropriate allowances for this when deciding what steps may be appropriate. However, if the initial assessment suggests a decline beyond expectation that may be causing functional difficulty, follow-up with more formal and rigorous assessments should be undertaken.
The physical examination is the first and fundamental part of the diagnostic procedure. Mobility, hearing and vision, that can confound later psychometric assessments, must be specifically included together with pulse, blood pressure and reflexes.
Laboratory assessments must be undertaken to exclude conditions such as those outlined in the table below.
The Dementia Syndrome
The next step is to establish the presence or absence of a dementia syndrome.
Abbreviated characteristics of the dementia syndrome as laid down in the DSM-IV are outlined below
There are a number of assessment scales that can be used to establish the presence of a dementia syndrome, but the one most commonly used is the Mini-Mental State Examination (MMSE).
The MMSE has been a mainstay in assessing cognitive decline: it remains widely used and is relatively practical for use by trained personnel both in primary and secondary care settings.
Performance on assessments such as the MMSE is sensitive to a patient’s prior intelligence, education, language and functional abilities. As a result, well-educated, intelligent individuals with strong language and compensating skills may give normal scores on the MMSE when the dementia syndrome is mild. Equally, individuals with relatively poorer prior abilities may achieve scores suggestive of a dementia syndrome when in fact there is none.
Moreover, impaired visual, auditory or motor function will also confound results. It is therefore important when assessing for dementia that thorough social, family and clinical histories are obtained, if not already available, and that a complete medical examination is undertaken to give a proper background to interpretation of the overall assessment.
Several techniques should be used as needed to identify or exclude some reversible causes of the dementia syndrome and, when degenerative dementia is probable, to differentiate these.
Commonly done assessments are described in more detail below.
Once blood tests have excluded certain possible causes of the patient’s symptoms, a brain scan is sometimes done. Less than 10% of cases in the UK and more than 70% in some European centres are referred for brain scans. Neuroimaging techniques, such as computerised tomography (CT) or magnetic resonance imaging (MRI) may show signs of vascular dementia, tumours, haematomas or normal pressure hydrocephalus (NPH) as a possible cause of dementia.
CT scanning is a radiographic technique that uses a computer to assimilate multiple X-ray images onto a two-dimensional cross-sectional image. This helps reveal the structure of the brain, and hence any abnormalities that may be present. MRI uses the influence of a large magnet to polarise hydrogen atoms, summate their spinning energies and uses these data to produce images of the brain.
Both CT and MRI are structural scans showing the anatomical structure of the brain and allowing morphological changes to be evaluated over time. Of the 2 techniques, MRI is more sensitive. It is important to remember that a normal CT or MRI does not rule out dementia at an early stage.
In addition to these scanning methods, techniques such as positron emission tomography (PET) and single photon emission computerised tomography (SPECT) can provide information about functional changes in the brain, i.e. changes in cerebral blood flow or changes in the metabolism of glucose or oxygen. PET is an imaging technique that uses short-lived radioactive isotopes to image the brain. It is a research rather than a clinical technique, which is available only in a few highly specialised centres. Typical images are shown below.
PET images of brains showing dementia
DAT = dementia of the Alzheimer type
In comparison with CT, MRI and SPECT, PET is expensive, seldom accessible and time consuming. Consequently, PET is not routinely used in the diagnostic workup for Alzheimer’s disease (AD). However, PET images may provide useful differential diagnostic information, such as parietal lobe changes in AD, when CT and MRI scans fail to provide sufficient information.
A number of rating scales have been developed that can initially be used in the diagnostic workup and thereafter in tracking and managing the progression of the disease.
These rating scales can be divided into five main types:
Psychologists may be involved in the investigation of dementia. It is the role of the psychologist to perform neuropsychological tests and evaluate the capability of the patient and caregiver to cope with their situation. The psychologist may be specialised either in old age psychology, gerontopsychology or in neuropsychology.
A 12-lead EEG, which reflects the electrical activity in the brain can also be used. A person’s EEG trace can be compared with a normal or expected result to establish whether or not there are abnormalities. The EEG may be normal in the early stages of AD, but abnormalities will appear as the disease progresses and becomes more apparent.
A lumbar puncture may be performed to gain further information that may help in the diagnosis. A lumbar puncture is a procedure in which a needle is introduced into the spinal canal, and cerebrospinal fluid (CSF) is collected for examination.
In certain diseases, changes in the CSF may reflect pathological processes in the central nervous system (CNS). Routine tests on the CSF include analysis of glucose, protein and blood cells. In specific cases immunoglobulin G (IgG) levels and the presence of borreliosis and tumour cells may also be investigated, and in research beta amyloid (Ab) and tau protein levels are studied.
Ab is a protein that forms thick deposits or plaques in the brains of patients with AD. This also occurs to a much lesse extent in the normally ageing brain. Lower levels than normal or soluble Ab (Ab42) in the CSF is suggestive of AD.
Tau protein is associated with the microtubules (part of the cytoskeleton) of the neurons. In AD, neuronal degeneration leads to formation of neurofibrillary tangles and release of tau protein into the CSF. Elevated levels of tau protein in the CSF suggest AD or some other form of dementia.
These exciting developments are still at the research stage and currently lumbar puncture is rarely performed as part of the differential diagnosis of dementia syndrome. However, in the future this may become an important part of the investigation process.
Last updated: 20.12.2011