Dementia

What is dementia?

Dementia is a collective name for the phenomena that occur in a number of brain disorders of which Alzheimer's disease is the most common. It involves symptoms such as memory loss, changes in behaviour and difficulties with orientation.

The core criterion adopted by DSM-V is 'the development of multiple cognitive disorders'. These are memory disorders in combination with one or more specific cognitive disorders. ¹²⁸

There are several risk factors for dementia, the main ones being older age, genetic predisposition, cardiovascular disease, type 2 diabetes, smoking, elevated cholesterol, arrhythmias (atrial fibrillation), excessive fat consumption, Parkinson's disease, Huntington's disease, Down syndrome, HIV and possibly excessive alcohol use. ¹²⁹

What are the complaints associated with dementia?

Memory disorders are characterised by a reduced ability to learn new information or to remember what has been learnt in the past. The specific cognitive disorders are aphasia (the inability to express oneself well verbally or in writing and/or no longer being able to understand spoken or written language adequately), apraxia (the inability to complete purposeful actions), agnosia (the inability to recognise objects) and the impairment of performal functions (inability to make abstractions, draw logical conclusions, organize, plan or act purposefully).

Additional symptoms associated with dementia can include: depressive mood, anxiety and apathy, hyperactivity (restlessness and agitation) and psychosis (delusions and hallucinations).

Various types of challenging behaviours – such as aggression, fits of temper, pica, self-injurious behaviour, shouting, walking away and repetitive behaviour – are seen in people with intellectual disabilities and dementia, sometimes at an early stage. ¹³⁰

How common is dementia in the general population?

The prevalence rate for dementia in general practice is 1.7%. The annual incidence rate is approximately 2 people per 1000 and it rises sharply with age. ⁴⁸⁴

Dementia is predominantly seen in older people: the Delphi study ¹²⁹ showed that, in Western Europe, 5.4% of the population aged 60 years or over had dementia (60 to 64 years: 0.9%; 65 to 69 years: 1.5%; 70 to 74 years: 3.6%; 75 to 79 years: 6.0%; 80 to 84 years: 12.2%; > 84 years of age: 24.7%).

How common is dementia in people with intellectual disabilities?

A distinction can be made here between people with and without Down syndrome.

An English study of 281 people aged 60 years or over with intellectual disabilities but without Down syndrome found a prevalence of 13.1% (in people aged over 60 years) and 18.3% (in people aged over 65 years).

This is 2 to 3 times higher than in a comparable age group in the general population. Higher age was a risk factor but there was no correlation with the severity of intellectual disability. ¹³¹

An American study of 126 people without Down syndrome found a prevalence rate for dementia that was the same as the prevalence rate for the general population. ¹³²

Prevalence rates for dementia in people with intellectual disabilities with Down syndrome varied between different studies looking at intramural settings. Haveman found dementia in 7% (people aged 40 to 49 years) to 65% (in the age group of 60 to 69 years) of the people with Down syndrome included in the study. ¹³³

In a prospective study of 306 people with Down syndrome, Visser found that the diagnosis of dementia was made at an average age of 56 years. Prevalence increased from 11% (40 to 49 years) to 77% (60 to 69 years). All people aged 70 years and over in this study had dementia. ¹³⁴

A large English study compared the general-practice files of 14,751 people with intellectual disabilities with those of 86,221 people without. The prevalence of dementia in the group with intellectual disabilities was 7.5%, which was significantly higher than prevalence in people without. ⁴⁸⁵

Other English research looking at general-practice databases found that dementia was present in people with Down syndrome aged 30 and over. The incidence rate is 92 times higher in this group than in the general population of the same age. ⁴⁸⁶

Another study shows that the prevalence rate for dementia in people with Down syndrome is 16.8%. ⁴⁸⁷

1.70% General population

13.1% to 18.3% People with intellectual disabilities (without Down syndrome) > 60 years

65% People with intellectual disabilities and Down syndrome between the ages of 60 and 69 years

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Diagnostic and Statistical Manual of Mental Disorders (DSM) is een Amerikaans handboek voor diagnose en statistiek van psychische aandoeningen. De huidige versie is een tekstrevisie van de vierde editie.

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