The diagnosis of dementia is based on a decline in cognition from a previous level of ability, observed both subjectively and objectively on cognitive testing, and is classified by the presumed underlying cause (see Differentiating types of dementia below). In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), dementia, which formed a category called “Delirium, dementia, amnestic, and other cognitive disorders” in DSM-IV, falls under the new category of “major neurocognitive disorders” (American Psychiatric Association, 2013).
DSM-5 outlines two core features of major neurocognitive disorder. The first is cognitive decline in one or more cognitive domains (attention, executive function, memory, learning, language, perceptual motor or social cognition). Evidence of this decline must come from two sources: concern expressed by the patient or another reliable source about cognition, and impaired performance on cognitive tests. The second core feature is impairment that interferes with the patient’s independence in everyday functioning.
Differentiating types of dementia
- Most common dementia, accounting for 50 to 60 per cent of all cases
- Characteristic gradual onset with progressive decline
Dementia with Lewy bodies
- Second most common type of dementia
- Associated with visual hallucinations, Parkinsonian motor symptoms, marked fluctuation in cognition or level of consciousness, sensitivity to extrapyramidal side-effects of antipsychotic medication
Vascular cognitive impairment and vascular dementia
- May be caused by a single large stroke or an accumulation of multiple subcortical strokes
- Often associated with Alzheimer’s dementia (mixed dementia)
- 30 percent of people who have had a stroke progress to dementia.
- Early loss of social skills, disinhibited behaviours, apathy and loss of insight
- Often has earlier onset than other dementias, and is often associated with family history of frontotemporal dementia