Cognitive Assessment


Cognitive Assessment

Cognitive assessment involves examination of higher cortical functions, particularly memory, attention, orientation, language, executive function (planning activities), and praxis (sequencing of activities). This article will focus on cognitive assessment of older people (those aged over about 65 years) in the context of possible dementia, delirium, and depression.

These are common and serious clinical syndromes affecting older people, and accurate cognitive assessment is an essential component for diagnosis. Dementia affects 20% of people aged over 80 years, and delirium may affect 30-50% of older people in hospitals and an estimated 16% in long term care facilities. The annual incidence of major depression in the general older population is about 15% a year and doubles after age 70.

Why does cognitive assessment matter?

Cognitive assessment helps to clarify the presence of one or more of the clinical syndromes of dementia, delirium, and depression. The abrupt change in mental state with reported sleepiness is highly suggestive of delirium, with a urinary tract infection (new onset incontinence) as a possible trigger. Dementia or depressive illness (loss of interest, poor concentration, forgetfulness), or both, are also possible so need consideration, but the immediate priority is to assess for delirium.
Patients with dementia have a very high risk of developing delirium (often triggered by an infection, surgery, or drugs), and delirium is often associated with progression of dementia.

Conversely, patients without baseline dementia who present with delirium may develop persisting cognitive deficits and effectively a new onset of dementia. Depression in older people often presents with complaints of memory impairment, and people with dementia may have an associated depression.

Cognitive assessment helps to clarify the presence of these syndromes. Currently many older people presenting with dementia, delirium, and depression do not receive a diagnosis, or they receive a misdiagnosis. In a 2010 observational study, only 25% of patients with delirium presenting to a medical assessment unit received a correct diagnosis. Failure to detect delirium may mean missing a treatable condition (such as a chest or urinary infection, or a drug side effect), which may be life threatening as every 48 hours spent with delirium is associated with an 11% increase in mortality. Hence, patients presenting with rapid (hours, days) onset of cognitive symptoms or a worsening of established symptoms should be assessed urgently for delirium.

The timely recognition of dementia when symptoms are causing anxiety to the patient or carer brings the possibility of better support, anticipatory care, initiation of drug treatment, and reduced distress for the patient and their carers. Failure to detect depression denies the opportunity for identifying a potentially treatable and debilitating illness. Depression in older people is just as treatable as in younger people.

What is the best way to assess cognition?

The key to the reliable identification of cognitive impairment is to integrate three components:
1) Observation of the Patient.
2) A Collateral Account from a Carer.
3) The results of Standardised Tests.
These components should consider key questions for immediate and ongoing management.

Observation of the Patient

The clues to the presence of cognitive impairment may be subtle and are often overlooked, particularly in dementia, where the onset may be insidious, with the family adapting to the impairments, regarding them as “normal” behaviour. The discussion with the patient can be sensitively directed to inquiries about intrusions into everyday life, such as forgetting appointments, problems with finances, mislaying objects, and kitchen mishaps. There may be indicators of personal neglect—sometimes obvious (such as a dishevelled appearance), sometimes less so (a mis-buttoned jacket in a previously fastidious man, or a usually immaculate lady who has left off her lipstick). The primary care practitioner, who may have known the person for some years, is particularly well placed to notice these. Close attention to the content, organisation, and presentation of the patient’s narrative is critical.

Points to look out for:
• Dementia—Features include impaired fluency of language, vagueness with dates and sequence of events, a tendency to repeat phrases, or a predilection to dwell excessively on distant events.
• Delirium—Features include poor attention (such as seemingly not following questions; distractibility; or inability to focus), incoherent speech (hard to fully understand what the patient is trying to say), and altered level of alertness (sleepiness or agitation). The key is substantial change or fluctuation in mental status over hours or days: this is the cardinal feature of delirium.
• Depression—Features include low mood, loss of interest and diminished capacity for enjoyment, poor self care, and a negative outlook with feelings of hopelessness that can include suicidal thoughts.

However, it is important to be aware that these features are less prominent in older patients, in whom somatic symptoms (reduced energy, poor appetite, insomnia) are more typical. Drugs are a common cause of delirium in older people, and a medication review is therefore essential. A systematic review of 14 randomised controlled trials and observational studies showed that opioids, benzodiazepines, and dihydropyridines (such as amlodipine)—and possibly antihistamines (H1 antagonists)—confer an increased risk of delirium. Digoxin and antipsychotics confer no increased risk, and uncertainty remains for other drug classes.

Examination should specifically assess for nutritional status (evidence of self neglect) and for uncorrected visual and hearing problems (easy to resolve and risk factors for delirium and depression). Examination should also assess for new physical illness (such as anaemia and cardiac or respiratory failure) or deterioration in a pre-existing chronic disease, as these are possible aggravating factors for dementia or depression or precipitants for delirium. For suspected delirium, focus the examination on detecting chest, urinary, and skin infections; heart failure and new or fast atrial fibrillation; urinary retention; and rectal examination if impaction is suspected.
In suspected dementia perform a neurological examination to assess for abnormalities in the pyramidal pathway (brisk reflexes and extensor plantar responses may indicate vascular dementia) and the extra-pyramidal system (expressionless face, bradykinesia, and cogwheel rigidity may indicate dementia with Lewy bodies). Investigations The investigations for suspected dementia, depression, and delirium are similar (box 2) but have different rationale. For dementia the aim is to detect potentially reversible causes for the cognitive impairment; for depression to identify physical problems that might be contributing to the low mood; and for delirium, to identify possible precipitants. Brain imaging is recommended for suspected dementia to identify the very few people with intracerebral tumours or normal pressure hydrocephalus, and to contribute to the diagnosis of the specific dementia type.

Collateral Account from Carer

A collateral account from a carer is essential for clarifying what the symptoms are, their timescale (weeks or months for dementia and depression, and hours or days for delirium), and their relation to baseline mental function. Again, a primary care practitioner who is familiar with the person is often better placed than a practitioner in secondary care, who must purposefully seek collateral information. Failure to undertake this straightforward task may result in misdiagnosis. Informant based questionnaires or the short form of the informant questionnaire on cognitive decline in the elderly may be used to structure the conversation.

They are both simple and quick to complete (three and five minutes respectively), either face to face or over the telephone. The questionnaires focus on long term changes in aspects of cognitive function and behaviour rather than current function and are thus less influenced by a person’s cultural and educational background and can reliably contribute to the diagnosis of early, mild, or more severe dementia.

Reports of recent changes in usual behaviour as an indication of delirium should also be specifically sought in any older person who is unwell. Indeed, the question, “Do you think [patient’s name] has been more confused lately?” had 80% sensitivity for delirium.

Standardised Assessments

Although the routine use of standardised assessment instruments is recommended, they are not diagnostic instruments—the diagnosis of dementia, delirium, and depression is eventually a clinical one that synthesises all available evidence. Indeed, the testing process can sometimes be more diagnostically informative than the actual test score achieved because it provides insights into cognitive processes such as attentiveness and disorganised thinking.

“Untestability” is itself an important sign of severe disturbance of the mental status and often indicates delirium. No consensus has been reached on which standardised assessments to use, but by becoming thoroughly familiar with and competent in the use of a few core instruments and basing this selection on local use, practitioners can maximise communication between teams. The reliability of responses on brief standardised assessments of depression can be reduced in people with moderate to severe cognitive impairment. However, coexisting depression is common, and if any uncertainty remains, consider referral for specialist assessment.

Brief Cognitive Tests

Many brief, standardised tests of cognitive function have been developed, mostly assessing memory and orientation. The test scores may help to gauge dementia severity and progression, and repeated scores (such as preoperatively and postoperatively) can also help with the diagnosis of delirium, especially if superimposed on dementia. Falsely low scores may arise in people with a low educational background, deafness (through mishearing questions), or depression (no interest in questions). The tests need to be conducted with sensitivity to prevent undue distress. Some commonly used tests are described below.

Mini-Mental State Examination

The mini-mental state examination is a widely used, well validated, 30 point cognitive test that comprises 11 items and takes about eight minutes to complete. It has a low ceiling, so people with mild cognitive impairment may score in the “normal” range of 25-30 points, particularly if they have high educational attainment. Scores of 21-24, 10-20, and 9 or less indicate mild, moderate, and severe cognitive impairment respectively. However, copyright protection is now enforced, and the mini-mental state examination must be purchased from the publishers. Abbreviated mental test score This 10 item assessment is commonly used in hospitals, although it has lower sensitivity and specificity to detect cognitive impairment than the mini-mental state examination.

A four item version of the 10 item test (known as the four item abbreviated mental test score) is used in emergency departments or acute assessment units, and its performance seems broadly equivalent to the full version; completion of this shorter abbreviated version takes less than one minute, and failure on any of the four items (age, date of birth, place, and year) implies cognitive impairment.

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