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.
Keywords: Alzheimer’s dementia, Down syndrome, diagnosis, diagnostic
instruments, intellectual disability, scales, screening.
