In this study, the prevalence of neuropsychiatric symptoms was estimated according to cognitive category, including severity of dementia, using a nationally representative sample of older adults in the United States, and greater risk for the presence of symptoms was found in those with more advanced cognitive impairment. A greater number of neuropsychiatric symptoms was independently associated with functional limitations in those with CIND and dementia, even after controlling for other potentially confounding factors. Individual neuropsychiatric symptoms that were most strongly associated with functional limitations in those with CIND and dementia were also identified.
The prevalence estimates are comparable with prior population-based estimates, after considering some methodological differences.1,16,17
It was estimated that 57% of those with dementia had at least one neuropsychiatric symptom, which was nearly identical to a prior study that used a similar methodology (56.2%)17
but lower than another study (74.6%),1
probably because two additional common symptoms (sleep difficulties and appetite or eating problems) were included. The estimate of the prevalence of any neuropsychiatric symptom in those with CIND or MCI and normal cognition was also lower than this prior study (44% vs 51% in those with CIND or MCI, 18% vs 27% in those with normal cognition). Agitation, apathy, and aberrant motor behaviors were the most common neuropsychiatric symptoms in those with severe dementia and were some of the symptoms that these individuals with difficulty communicating could exhibit and their informants could observe.
To the authors’ knowledge, this is the first study to examine the relationship between number of neuropsychiatric symptoms and presence of individual symptoms and ADL and IADL limitations and to considering the clinical significance of the symptoms and adjust for cognitive category, including dementia severity. A greater number of neuropsychiatric symptoms may lead to ADL and IADL limitations as a direct consequence of the symptoms themselves, or it is possible that neuropsychiatric symptoms are a reflection of worse cognitive impairment even within cognitive categories. Impairment of executive control functions, which has been suggested as a cause for functional limitations,40–42
may confound this relationship. Other physical illnesses, not controlled for in this study, for example Parkinson’s disease or limb amputation, may be associated with neuropsychiatric symptoms (e.g., depression, psychosis, apathy) and ADL limitations. Regarding the association between individual neuropsychiatric symptoms and functional limitations, the findings were somewhat different than in prior studies, again probably because of differences in methodology. Although a prior study found psychosis (delusions and hallucinations) to be associated with more-significant functional limitations,25
the current study found that this relationship was not significant after adjusting for co-occurring neuropsychiatric symptoms and chronic medical conditions. Other symptoms that were independently associated with functional limitations (depression, anxiety, and aberrant motor behaviors) were identified when these symptoms were clinically significant.
The strengths of this study include a nationally representative population-based sample that included the whole spectrum of cognitive function and the use of a well-validated comprehensive assessment of neuropsychiatric symptoms. A number of potential limitations should also be considered when interpreting the results. Some remaining nonresponse bias might have affected the analyses despite the use of ADAMS sampling weights, which attempted to account for differential nonresponse. Measurement error for neuropsychiatric symptoms may have occurred even though the NPI has been shown to have good psychometric characteristics.36
ADAMS interviewers assessed the reliability of informants; 83%, 13%, and 1.3% of informants were rated as very reliable, probably reliable, and not reliable, respectively. Assessment of functional limitations may also be subject to measurement error because suboptimal reliability between informant report and directly observed limitations has been suggested in prior studies.43
In summary, neuropsychiatric symptoms are common in older adults with CIND and dementia in the United States and are associated with a significantly higher level of ADL and IADL limitations. Future research aimed at better understanding how neuropsychiatric symptoms affect function may help in the design of interventions to better manage neuropsychiatric symptoms and reduce their burden on patients, families, and the healthcare system.