The assessment of cognitive decline

An understanding of alterations in cognition with age can help GPs detect impairment, writes Professor Steve Iliffe.

Cognitive funstion tests in mild cognitive impairment may help but are not diagnostic
Cognitive funstion tests in mild cognitive impairment may help but are not diagnostic

The National Dementia Strategy, published in February 2009, proposes a public awareness campaign that will encourage people who are worried about their memory to seek advice from their GP.

Such publicity will lead to an increase in demand for advice about memory loss. An understanding of how cognition alters with ageing can help GPs solve diagnostic problems.

Four types of memory can be defined: episodic memory is memory of specific past events that involved the person; semantic memory is the store of facts and general knowledge; implicit memory is the non-conscious part of memory that uses past experience to shape current behaviour; and executive functioning involves the forms of thinking necessary for goal-directed behaviour.

The difference between normal brain ageing and the kind of cognitive impairment that leads to 'brain failure' (dementia syndrome) are shown in the figure below.

The red line shows the slow deterioration that occurs in overall cognitive function as we age. The sudden change represents acute illness at the end of a healthy, active life. In normal ageing, mental faculties are retained, but memory and thinking are slower.

The range of normal cognitive functioning widens with ageing, making it difficult to identify those whose brains are failing more rapidly.

The blue line in the figure shows the trajectory followed by those who will eventually develop a dementia syndrome. Phase A may last a decade during which cognitive functions deteriorate more than would be expected.

There is no accurate way clinically to identify those who will develop dementia syndrome.

Phase B is a decompensation phase in which global cognitive deterioration occurs, affecting episodic memory, executive function, verbal ability, visuo-spatial skills and attention. The changes may be subtle, and may be attributed to depression rather than cognitive failure.

Mild cognitive impairment
Phase C is a period of relative stability. Compensation may occur with recovery of neuronal networks, and relatives may, for example, take over the management of diaries or finances.

The transfer of information from temporary to permanent memory decreases. This phase corresponds to the idea of mild cognitive impairment (MCI).

The patient has subjective symptoms (predominantly of memory loss) and measurable cognitive deficits, but everyday life may not be affected. The considerable overlap in cognitive performance between normal ageing and MCI nevertheless makes routine screening in primary care impractical.

Subjective impairment of memory is strongly associated with depressed mood, and most patients who consult their GP with memory complaints do not have dementia. However, depression is itself a risk factor for dementia, making the diagnostic task even more difficult.

Talking to partners and carers can be helpful. Ask if the patient has more trouble remembering things that have happened recently, has trouble recalling conversations after a few days, and has difficulty in word selection or tend to use the wrong words.

Also ask if the patient is less able to manage money, has problems managing medication, and needs more help with transport.

Making the diagnosis
Phase D is the beginning of a precipitous decline in cognitive function, lasting between two and five years. In addition to the cognitive deficits that have already occurred, semantic memory and implicit memory become impaired.

Diagnosis tends to occur at point D2 in the figure, some months after the precipitous decline begins. Patients survive an average of three and a half years from this point.

There is evidence that early recognition and intervention at the D1 point may allow earlier symptomatic treatment for those with the Alzheimer's subtype and delay the move to a care home.

A modified form of global assessment may help confirm an initial suspicion of dementia.

Table 1 shows a condensed form of global assessment that seems workable in general practice, without the need for a scoring system. The most important column for GPs is the middle one, which lists early features.

Cognitive function tests can help, but none are diagnostic. It may be easiest to use the one that your old age psychiatrist recommends.

They might not want you to use the mini mental state examination, because repeated use 'trains' patients and can cause misleading results.

Disclosing the diagnosis
This is not an event, but a process. Some patients with cognitive impairment will not want to know, and GPs must accept with and work around this denial.

Others may anticipate that they will be pushed onto an escalator to disability if they seek an answer to their memory problems, and hope to safeguard their driving licence or sense of self by not asking for help.

A small number will have lost insight as part of the disease process, and insist that the problem lies with 'difficult' family members. GPs will have little choice but to wait patiently for the situation to change while keeping dialogues going.

  • Professor Iliffe is professor of Primary Care for Older People at University College London, and chief investigator on the EVIDEM (Evidence-based Interventions in Dementia) programme (evidem.org.uk). The EVIDEM programme receives financial support from the National Institute for Health Research (NIHR) Programme Grants for Applied Research funding scheme. The views and opinions expressed in this editorial do not necessarily reflect those of the NHS, the NIHR or the DoH.

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