Assessment and diagnosis of dementia (2024)

Diagnostic criteria for cognitive impairment and dementia

Dementia is the umbrella term for a number of neurological conditions, of which the major symptom is the decline in brain function due to physical changes in the brain. It is distinct from mental illness.

Dementia is categorised as a Neurocognitive Disorder (NCD) in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). The NCD category is then further subdivided into Minor NCD and Major NCD. The term “cognitive” refers to thinking and related processes, and the term “neurocognitive” has been applied to these disorders to emphasise that brain disease and disrupted brain function lead to symptoms of NCD.

The NCD category encompasses the group of disorders in which the primary clinical deficit is in cognitive function, which is acquired rather than developmental. Impairment may occur in attention, planning, inhibition, learning, memory, language, visual perception, spatial skills, social skills or other cognitive functions.

Minor neurocognitive disorder

In DSM-5, a minor neurocognitive disorder is also medically referred to as Prodromal Disease or Mild Cognitive Disorder (MCI) and is defined by the following criteria:

Major neurocognitive disorder

In DSM-5, a major neurocognitive disorder is defined by the following:

There is evidence of substantial cognitive decline from a previous level of performance in one or more of the domains listed below, based on the concerns of the individual, a knowledgeable informant, or the clinician; and a decline in neurocognitive performance, typically involving test performance in the range of two or more standard deviations below appropriate norms (i.e. below the third percentile) on formal testing or equivalent clinical evaluation.
The cognitive deficits are sufficient to interfere with independence (i.e. requiring minimal assistance with instrumental activities of daily living).
The cognitive deficits do not occur exclusively in the context of a delirium.
The cognitive deficits are not primarily attributable to another mental disorder (for example major depressive disorder and schizophrenia).

Cognitive domains

The DSM-5 details six cognitive domains which may be affected in both Minor and Major NCD:

Complex attention

Involves sustained attention, divided attention, selective attention and information processing speed

Warning signs - Patient has increased difficulty in environments with multiple stimuli (TV, radio, conversation). Has difficulty holding new information in mind (recalling phone numbers or addresses just given or reporting what was just said)

Executive function

Involves planning, decision making, working memory, responding to feedback, error correction, overriding habits and mental flexibility

Warning signs:

Patient is unable to perform both familiar and complex tasks and projects (at work and at home).
Needs to rely on others to plan instrumental activities of daily living or make decisions.
Has problems with abstract thinking, displays loss of initiative as well as poor/decreased judgement.

Learning and memory

Involves immediate memory, recent memory (free recall, cued recall and recognition memory) and long term memory

Language

Involves expressive language (naming, fluency, grammar and syntax) and receptive language

Warning signs:

Patient has significant difficulties with expressive or receptive language.
Often uses general terms such as 'that thing' and 'you know what I mean'.
With severe impairment may not recall names of closer friends and family.

Perceptual-motor function

Involves picking up the telephone, handwriting, using a fork/spoon

Warning signs:

Patient has significant difficulties with previously familiar activities (using tools or, driving a motor vehicle) and navigating in familiar environments.

Social cognition

Involves recognition of emotions and behavioural regulation, social appropriateness in terms of dress, grooming and topics of conversation

Warning signs:

Patient may have changes in behaviour (shows insensitivity to social standards, or make decisions without regard to safety).
Patient usually has little insight into these changes. Becomes socially withdrawn or isolated.

ICD-11 coding for dementia

The International Classification of Diseases (ICD) is the standard diagnostic tool for epidemiology, health management and clinical purposes. You can find ICD-11 codes on the WorldHealth Organisation’s ICDwebsite.

Assessment for cognitive impairment and dementia

There is no single definitive test for diagnosing dementia. Assessment will account for behavioural, functional and psychosocial changes, together with radiological and laboratory tests. The assessment process may take three to six months.

Assess cognition if you have any indication or suspicion of impairment in your patient. This is the first step in determining whether or not your patient needs further evaluation.

Take notes about the history of the patient from an “informant”: someone who knows the patient well and has observed their cognition and function over time. They might be a partner, family member or close friend.

You could ask the informant about the following in relation to your patient:

risk factors: vascular disease, alcohol, head injury, mood disorders, behavioural and psychological symptoms, recent illness, medications
Activities of Daily Living (ADL), instrumental ADLs, cognitive complaints, mood, driving, safety
behavioural changes and functional decline (time course = onset, progression)

One useful tool for interviewing informants is the AD8Dementia ScreeningInstrument.

The following cognitive assessment tests are the most commonly used; however, it is important to choose the tests most suitable for your patient and for the health setting within which you work.