Dementia in people with intellectual disability

Approximately 13% of people with intellectual disability over the age of 50 years have dementia, which is a much higher rate than that found in the general population. Testing for dementia involves asking questions to test mental function. These include asking how old the person is, seeing if they know the date, time and where they are, as well as simple spelling and mathematical tests. In people with intellectual disability it may be difficult to decide if their difficulties in answering questions are due to the intellectual disability or the onset of dementia. In addition, the decline in function may be inadvertantly hidden by carers who compensate by increasing the amount of support they give to the person.  To make a diagnosis of dementia it is important to establish what the person is normally capable of to get a sense of how they should perform in this type of testing. This is done by establishing a ‘baseline’ that formally records a score that indicates the person’s normal level of function and can be used as a reference point for comparison. Often these tests look at what a person can do as well as well as what questions they can ask. Carers have a vital role in providing information about what a person can usually do, which is essential in determining if there has been any change. Often the first sign of dementia that is noticed by others is forgetfulness. Initially this involves recent events or conversations so the person may forget what they have just eaten or the conversation that they have just had. They find it difficult to remember the names of people they have just been introduced to.  Difficulty in naming everyday things such as a pen is also common. This may not be obvious in people with intellectual disability and the first signs may be getting lost in familiar places, not recognising people they previously knew or not being sure how to complete a familiar job at day placement or task such as laying the table or getting dressed. Other problems can include increasing clumsiness and difficulty in doing up shoe laces or buttons. An exacerbation of epilepsy or starting to have fits for the first time may be the first sign of dementia. As the dementia progresses the picture is very similar to the normal population with a gradual decline in abilities that can be associated with a range of behavioural and psychiatric problems such as aggression, irritability, anxiety, paranoia and hallucinations. Dementia in Down Syndrome People with Down Syndrome are at a particularly high risk of dementia and it tends to occur at a much younger age, thirty or forty years before the general population. Over 40% of people with Down Syndrome will develop dementia in their forties. The illness also progresses more rapidly with an average time from diagnosis to death of 4.6 years. Given the high risk, it is suggested that people with Down Syndrome have routine assessments of their cognitive and functional ability in adulthood to aid with future assessments.