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What are the diagnostic criteria for dementia?

Updated: Nov 11, 2021

Dementia describes a collection of symptoms that are caused by a group of neurological disorders affecting the brain function. Dementia is an umbrella term and is not one specific disease. The are several types of dementia, for example, Alzheimer's disease, vascular disease, Lewy Body Dementia, Parkinson's disease dementia and frontotemporal dementia.

If someone has dementia that means all the following statements about them are true.

1. There is impairment in one or more types of mental functions (cognitive domains)

When we talk about dementia, most people think it is loss of memory. They are correct. Typically, it is the short-term memory that is affected, and patients may forget what they have been told ten minutes ago and may have difficulty in learning new skills, while distant memories are preserved so they may be able to recall something important that happened 30 years ago. There are other cognitive functions that are affected in dementia such as language, executive function, complex attention, visuospatial function, and social cognition. While memory is commonly affected sometimes it may be spared in early stages some forms of dementia, such as frontotemporal dementia.

2. The difficulties represent a decline from the person’s prior level of cognitive ability

Dementia is a change compared to a person’s previously known cognitive abilities as an adult. For example, families or friends may notice fading memory in someone who used to be very sharp and had good memory. People with emerging dementia may start to forget where they put belongings, forget names of people whom they know reasonably well, forget important conversations and/or repeat them, miss important appointments and forget to take medications on time. On the other hand, some people may have had lifelong problems with reading or math or even social graces, and unless there had been a change (worsening) we should not attribute them to dementia as they get old.

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3. The problems are bad enough to impair daily life function and independence

It’s not enough for a person to have an abnormal result on an office-based cognitive test administered by a geriatrician or another clinician. The problems also have to be substantial enough to affect how a person manages usual life, such as work and family responsibilities. Usually, the difficulties start with complex tasks first, such as managing bills, taking medications, driving, shopping, cooking and housekeeping (which are called instrumental activities of daily living). On the other hand, if the cognitive problems are insufficient to interfere with their independence because either they are modest, or the person is able to overcome them by putting greater effort or compensatory strategies such as using memory cues (reminders) then we cannot call it dementia (yet) - although we know this is not normal.

4. The problems are not due to a reversible condition or a mental health disorder

It is important that reversible causes and conditions that can produce as illness that may mimic dementia are investigated excluded, such as delirium, depression, psychosis, underactive thyroid or medication side-effects. This is usually needs taking a history, physical examination, blood and urine tests, and brain scans.

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