Dementia in People with Intellectual Disabilities

With the increasing life expectancy in the last five decades, people with intellectual disabilities (ID) are exposed to the risk of age-related neurodegenerative disorders including dementia. The prevalence of dementia is increased in people with ID compared with that in the general population. People with Down syndrome (DS) are at even a higher risk of developing Alzheimer’s dementia (AD) compared with non-DS people with ID. However, there are difficulties in making an early and accurate diagnosis of dementia in individuals with ID and the screening instruments such as the Mini Mental Status Examination that are used in the general population often show floor effects when used for individuals with ID because of their pre-existing cognitive impairment, the level of which varies depending on the severity of ID. Both informant-rated and direct neuropsychological tests have been used for the case detection of dementia for individuals with ID. However, direct neuropsychological tests cannot be used for those who have severe ID and their validity could still be questionable in a number of cases of mild to moderate ID. There are many similarities and some differences in the clinical manifestation of dementia in individuals with ID and the non-ID general population. Impaired recent memory and confusion in the context of relatively intact distant memory are likely to be the early symptoms in individuals with ID who have a mild ID, whereas loss of skills and change in behaviour are likely to be the early features for those with more severe ID. Many symptoms, including features of ‘frontal lobe dysfunction’ that tend to appear late in dementia in the general population, may appear early in individuals with ID and DS. Ideally, individuals with ID should be screened for signs of dementia from before the age of 30/35. A multi-disciplinary approach should be taken for diagnosis of dementia in individuals with ID using a combination of informant-rated scales and neuropsychological tests in a longitudinal fashion over time. Important differential diagnoses include hypothyroidism, depression, and sensory impairment. Assessment should include physical, psychological, and social aspects including appropriate examinations and investigations. The evidence-base for the pharmacological management of dementia in ID and DS is poor, which does not allow to draw any definitive conclusion about their efficacy in this population. Therefore, the same pharmacological regime that is used in the non-ID population along with non-pharmacological interventions should be considered for people with ID.