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Brain failure - MMSE limitations
Brain failure - MMSE limitations
Date Created: 18/02/2001 Last Modified: 02/01/2003 Last Checked: 20/01/2003
MMSE: limitations and use
When clarifying the presenting problem / complaint it is useful to remember the abnormal behaviours that are most frequent in dementia; these are:--
- verbal or physical aggression / aggressive resistance
- sadness / anxiety
- hypophagia
- disturbed diurnal rhythm
- getting lost
- persecutory ideas / hallucinations.
The above data comes from a recent prospective study where abnormal behaviours were assessed periodically over the course of the illness and the diagnosis of Alzheimer's was confirmed at post mortem. It is probably the 'best' data gathered so far. Generally speaking ‘behavioural’ observations have substantial advantages over psychometric tests (such as the “Mini mental state examination”) for the assessment of dementia syndromes. Behavioural observations are structured, standardised and scored observations of everyday activities such as, finding the way round a new building, ordering and remembering meals / staff members names and faces etc.
They have useful advantages over psychometric tests:--
- Most patients do not appreciate that they are being “tested”.
- Behavioural observations are at least as good, and sometimes better than, psychometric tests; especially in mild dementia.
- Behavioural observations usually give a better and more directly relevant measure of real life capabilities.
These, and other, observations made by doctors and the experienced trained staff on a memory unit enable a confident and reliable assessment.
Inpatient admission for workup is my strong preference. Admission allows longitudinal behavioural observations to assess, among other features, the degree of variation in level of performance and consciousness. That helps to distinguish the 20% or so of those who have Dementia with Lewy bodies.
The process of being tested with tests like the “Mini mental state examination” can, of itself, be distressing and may precipitate and aggravate distress. Consideration of the patients overall situation may suggest administering a “Mini mental state examination” is not useful prior to referral. This will be even more so if it is going to be repeated in a specialist clinic (see below). The MMSE, despite its widespread use, is of limited accuracy and validity. It was devised in the early 1970s. Its adoption as the de facto standard for many trials and for the purposes of getting approval for drugs is a compromise that probably reflects expediency.
Like any diagnostic test (eg thyroid function) remember that sensitivity and specificity depend on the frequency of occurrence of the condition in the population under consideration. In unselected general practice / community patient samples its sensitivity and specificity are low, and a cutoff of 20/21 may need to be adopted to avoid excessive false positives. The cutoff score for suspecting a diagnosis of dementia varies between 20 and 27, depending on various factors (see below). It performs particularly poorly when people have fewer years of schooling. It is not a sensitive index of change with altering levels of severity of disease or change due to treatment.
When used in general practice, where it might be hoped the test would distinguish between mild cases and non-cases, it performs poorly and is of questionable usefulness.
The typical improvement of MMSE scores in trials of drugs (eg donepezil and rivastigmine) is a mean of 1.3 points over 12 weeks. The test retest and inter-rater reliability fall considerably short of that necessary to detect such a change; indeed a change of 3-5 points may go undetected.
There are many widely used sets of criteria for the diagnosis of dementia.
Recently a comparison of six commonly used classification systems including:-- DSM-III, ICD-10, CAMDEX has been made.
The proportion of subjects with dementia varied from 3.1 percent with ICD-10 to 29.1 percent with DSM-III.
The six classification systems identified different groups of subjects as having dementia. Many doctors may be astonished that out of the total of 1,879 cases only 20 of the cases were given a diagnosis of dementia according to all six systems. These sets of criteria for the diagnosis of dementia differed by a factor of 10 in the number of cases classified as having dementia.
The features that most frequently caused disagreement in diagnosis were:--
- Long-term memory
- Executive function
- Social activities
- Duration of symptoms
All text ©Dr Ken Gillman MRC Psych - PsychoTropical Research®
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