8. Conclusion
In conclusion, BPSD are a core symptom of dementia in
addition to cognitive decline and impaired activities of daily
living, and are extensively studied in MCI and AD patients in
the general population. Despite the extremely high risk to
develop AD and the lack of early (bio)markers with limited
invasiveness to predict the onset of AD in DS, most dementia
research in the DS population did not comprehensively assess
BPSD. The great variety of cohorts, diagnostic methodologies,
covariates and outcome measures that have been used in the
available BPSD studies in DS yielded diverse results and made
comparisons generally hard to accomplish. Due to the multitude
of applied, sub-optimal scales, it is questionable whether
BPSD have always been accurately assessed, for instance
regarding the differential diagnosis between apathy and
depression. Inter-study comparisons are additionally
complicated by the fact that control groups varied between
these studies, from non-demented DS individuals and intellectually
disabled persons with other aetiologies, to AD patients
in the general population.
Various BPSD appear to be altered in demented DS individuals,
but study results have not always been consistent.
Based on the existing literature, Fig. 1 summarized the temporal
relationship between BPSD and the clinical diagnosis of
AD. From childhood to adulthood, externalizing behaviour
likely decreases and internalizing behaviour increases. Frontal
lobe symptoms have been suggested as early signs of AD in
DS. Indeed, disinhibition and apathy, as well as executive
dysfunction, seem to be omnipresent in the prodromal phase,
whereas reports are still too divergent to assume that this is
also true for depression. Regarding activity disturbances,
various studies indicated decreasing hyperactivity levels towards
adulthood in DS. Excessive activity in demented DS
individuals would thus be a fairly easy observable sign.
However, general slowness in this group has been reported as
well. In addition, the presence of apathy itself might cause
reduced activity. Agitation appears to be more prevalent in
demented than in non-demented DS individuals, but reports
on aggression are inconsistent, though aggression seems to be
reduced in the overall DS population. Sleep disturbances are
markedly present in both demented and non-demented DS
individuals. Although sleep disorders may not yet differentiate
between those with and without AD, they are important
to consider as such sleep disorders may aggravate cognitive
decline and BPSD. Next, a higher prevalence of psychotic
symptoms (delusions and hallucinations) is likely observed in
DS persons with dementia than among those without dementia.
Finally, anxiety and phobias, appetite and eating abnormalities,
and euphoria have been hardly studied in DS and
DSþAD.
Taken together, the need for a validated and comprehensive
evaluation scale for BPSD in DS is evident. The limited
current understanding and the vast amount of (inconsistent)
reports discussed in this review illustrate the vital importance