Context: In the 1930s the life expectancy of people with intellectual disability (ID) was less than 20 years. Today people with ID have a life expectancy of 60 years. People with ID have general and specific risk factors for dementia. People with Down syndrome (DS) are at particular of developing Alzheimer's disease (AD) in their 6th decade.
Objectives: To examine: the prevalence of dementia in people with intellectual disabilities; risk factors for dementia; clinical criteria for making a diagnosis of dementia in people with ID; clinical assessment of dementia in people with intellectual disability. The focus will be on assessing for AD in people with DS.
Key messages: Standard assessment protocols used in the general population are not valid for use in people with ID due to substantial floor effects. Nonetheless the pattern of progressive deficits seen in the general population with AD is also seen in people with DS and AD. Determination of baseline functioning and a demonstration of progressive decline in executive function, memory with rapid forgetting of new learning, language, visual-spatial and learnt motor skills using a modified protocol can lead to a valid diagnosis of Alzheimer's disease. Comorbid conditions including sensory impairments, medical and psychiatric disorder are common and may complicate the clinical picture.
Conclusion: The fundamental principles of diagnosis of dementia in the general population also apply to people with intellectual disability, however a different battery of assessment tools are required.
