There are difficulties in making an early and accurate diagnosis of dementia in individuals with DS; in 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 Down syndrome (DS) because of their pre-existing cognitive impairment, the level of which varies depending on the severity of intellectual disability (ID). Both informant-rated scales and direct neuropsychological tests have been used for the case detection of dementia for individuals with DS. 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. Therefore, use of informant-rated scales is desirable for screening purposes.
There are many similarities and some differences in the clinical expression of dementia in individuals with DS and the general population who do not have ID. Impaired recent memory and confusion in the context of relatively intact distant memory is likely to be an early symptom in individuals with DS who have mild ID, whereas loss of skills and behavior changes are likely to be an early feature for those with more severe ID. Many symptoms, including features of ‘frontal lobe dysfunction’ that tend to appear late in the dementing process in the general population, may appear early in individuals with DS. An important early sign is any change in behavior or functioning, and dementia must always be considered as a possible cause for the change.
Ideally, individuals with DS 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 DS 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 physical examinations and investigations.