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How Is a Diagnosis of Dementia Made?
The Diagnostic and Statistical Manual Fifth Edition (DSM-5) definition of dementia (re-named Major Neurocognitive Disorder in this classification) is of a significant cognitive decline from a previous level of performance in one or more cognitive domains. The decline should be sufficient to undermine independence in everyday activities and not occur exclusively in the context of delirium. The decline should not be explainable by another mental disorder.
The diagnosis of dementia can be complex and requires experience and time. National Institute for Health and Care Excellence (NICE) guidelines recommend that the diagnosis is made by specialist services and this implies that specialist referral should be considered in all cases of dementia. As some dementias are reversible, early referral is important; early diagnosis is recommended in the National Dementia Strategy.
NICE recommends several stages in the diagnosis of dementia
History: As many patients with dementia have reduced insight they may underestimate the problem so it is important to take a history from a suitable informant as well as the patient. The contrast between the story from a close informant and the patient's account is often the most useful part of the assessment. It is important to ensure that medication is not contributing to their problems.
Physical examination: Physical signs such as a visual field defect suggest a secondary dementia and may contribute positive information such as parkinsonian features in patients with dementia with Lewy bodies (DLB).
Cognitive examination: It is fundamental to the diagnosis of dementia that a deficit in cognition is identified.
Investigations: Imaging and other investigations can exclude secondary causes of dementia but may also produce positive support for a clinical diagnosis—such as hippocampal atrophy in Alzheimer's disease (AD).
It is also important to follow-up the patient. Patients with mild problems such as amnestic mild cognitive impairment (aMCI) may not progress.
In the mid-to-late stages of dementia the diagnosis can be easy to make and it is possible to omit some of these stages. The earlier the diagnosis is attempted the more difficult it becomes and the higher the risk of misdiagnosis. The key parts of the assessment are the history from the patient and an informant and the performance of the patient on cognitive testing.
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