To our knowledge, this is the first investigation involving large-scale screening for both dementia and geriatric depression simultaneously. The major findings of this study are threefold. First, there is a large proportion of suspected dementia among elderly outpatients in a university hospital. Second, the ratio of suspected depression is also notable for the same group of older adults. Third, there is a significant overlap between suspected dementia and suspected depression among this elderly group.
As shown in Table 1, there was a high AD8-positive rate (28.2%, suspected dementia) in our study, compatible with the previous reports of using AD8 in the hospital 22,23 but much higher than the AD8 screening results in the non-hospital settings 24,25. There are some possible explanations for the high positive rate of AD8 in our study. First, evidences have suggested that the prevalence of dementia varies greatly based on the setting, with the estimated rates in primary care and hospital being 1.4% and 15–42%, respectively 26,27, contributing to the difference in the positive rates of dementia screening. The elderly who visited the hospital must have more systemic diseases including diabetes mellitus, hypertension and dyslipidemia than the elderly in community and these age-related chronic illnesses have been suggested to increase the risk of dementia 28. Besides, because our screening program was conducted in a university hospital, patients visited here may have suffered from complicated disease for a period of time that may have even higher risk of dementia. Thus, it is reasonable to predict a higher positive rate of AD8 screening in our study. Second, being hospital-based screening with AD8, the former two studies recruited participants <60 years old with the median age and the mean age to be 66 and 69.9 years separately. On the contrary, only those ≥ 65 years were recruited in our study making the mean age much older than the previous investigations (77.2 years). And age is one of the established risk factors for dementia. Third, although studies have supported the effectiveness of AD8 in dementia screening, a recent Cochrane review suggested that the AD-8 has a higher relative sensitivity (1.11, 95% CI 1.02 to 1.21), but lower relative specificity (0.51, 95% CI 0.23 to 1.09), in secondary care settings compared to community care settings 29. This character may increase the positive rate of AD8 screening in the hospital settings. Fourth, besides of screening for dementia, AD8 has been reported to be effective in detecting MCI and very mild dementia 18,30. Thus, the elderly with AD8 screening positive in our study may include some MCI cases. In summary, AD8 screening in hospital-based settings showed significantly higher positive rate than community-based screening. The high sensitivity of AD8 in the secondary care settings29 suggests its effect in identifying adults who may benefit from further evaluation for dementia. AD8 is a screening tool, the diagnostic confirmation requires more detailed assessment including laboratory tests, brain image analysis and psychological testing etc., and all of these are available in the general hospital contributing to a better diagnostic facility.
Table 1 also showed that with the screening tool of BSRS-5, 15.0% of elderly outpatients were suspected depression. Compared with previous studies of using BSRS-5 in older adults ≧65 years, the positive rates for community and inpatients of medical or surgical conditions were 9.5%31 and 25.3%32 respectively. Our result suggested that the positive percentage for elderly outpatients was between these two rates. There used to be many studies investigating the prevalence of geriatric depression and the results vary depending on the definition of depression and on the target subsets of the elderly population. The terms used in geriatric depression include major depressive disorder, major depression, clinically significant depressive symptoms, and depressive symptom etc., which represent different severity, different definition or diverse tools of evaluation. Compared with using the DSM-V or ICD-10 criteria, the prevalence for investigations that used the depressive symptom checklist to define the clinical case of geriatric depression must be higher. And in general, the prevalence may be higher in the hospital-based settings than in the community. Along these lines, there were several rates of geriatric depression being reported before. In a community study of adults aged ≥65 years, Hasin et al., have reported the prevalence of major depressive disorder to range from 1–5% at any time 9. By contrast, in a review article, Blazer reported that the clinically significant depressive symptoms are present in approximately 15% of community-dwelling elderly people 10. Besides, the rates of major depression among elderly people had been reported to be higher in certain subgroups, including medical outpatients (5–10%) and medical inpatients (10–12%) 10,11. A study carried out in outpatient setting of geriatric clinics of tertiary care hospital using the Geriatric Depression Scale (GDS-15) showed a rate of 22% of participants scored high on the GDS (≥5) and 18% were definitely having a depressive disorder as per ICD10 33. It seemed that among elderly outpatients, the positive rate of BSRS-5 was lower than that of the GDS-15 but closer to the percentage of depressive disorder defined by ICD10. Further studies may be needed to get more information about the usage of BSRS-5 in the screening of depression among elderly outpatients. In summary, the notable positive rate of BSRS-5 among elderly outpatients in our study implies the cost-effect of performing the screening of geriatric depression for this group in order to detect the disease earlier and start treatment. At the same time, before diagnosing the geriatric depression, a series of survey is needed to rule out the possible existence of other organic lesions. And the hospitals just meet the needs which reinforce the benefit of implementing the screening program in the hospital-based settings.
The analysis of the effect of the participant’s gender suggested that after adjustment for age, the mean score for female is higher than male in both AD8 and BSRS-5 and with statistical significance. The results are compatible with previous investigations indicating that female is one of the risk factors for both dementia and geriatric depression 11,34. Besides, in Table 3, the analysis about the effect of the age on AD8 and BSRS-5 showed that the mean scores significantly increased with age in AD8 but not in BSRS-5. These findings are also compatible with previous reports which suggested age to be a risk factor for dementia but not for geriatric depression 34,35. The analysis regarding the effect of the elderly patients’ gender and age on AD8 and BSRS-5 are twofold. First, when elderly female with chronic illnesses is involved, clinicians should pay more attention to the tendency of both cognitive decline and depression. Second, although evidence indicates that depression becomes less common and less severe with age, the lower-severity depressive symptoms, which can also be consequential and treatable, should not be overlooked 36.
Besides of the high prevalence of suspected dementia and suspected depression among the elderly outpatients, our study furtherly suggested that there was a remarkable overlap between suspected dementia and suspected depression. In other words, to implement a screening program for both dementia and depression among elderly outpatients in a university hospital, there exists about 7% with positive results in both dementia and depression screening. Further analysis suggested that the overlap between suspected dementia and suspected depression had reached the statistical significance. These results suggested that, for the older adults in outpatient department, to perform the screening either for dementia or for geriatric depression alone may have some bias. Spearman’s rank correlation analysis in our study also implied that the instruments for dementia screening and for depression screening are not completely independent. Compared with the past investigations, there used to be little study to perform the large-scale screening for both dementia and geriatric depression at the same time. But this result is partially compatible with a current consensus that increasing evidence supports a linkage between dementia and depression 37,38. There are some possible explanations for the significant overlap between the suspected dementia and suspected depression in our study. First, evidences have suggested a high prevalence of depressive symptoms in dementia patients. In a study of Zubenko et al., depressive symptoms were reported in 30–50% of patients with Alzheimer disease, particularly at the prodromal stage 39. Furthermore, major depression was observed in >10% of patients with Alzheimer disease and in 20% of those with vascular dementia 40,41 suggesting a high ratio of positive results in both dementia and depression screening. Second, although being an old concept, the key role of depression, especially that has not been diagnosed and without treatment, in the background of pseudo-dementia may also contribute partially to the overlap between suspected dementia and suspected depression 42. Third, cognitive deterioration and depression may share some of the common etiology contributing to their cooccurrence. Several mechanisms have been proposed to explain the connection between depression and dementia of which vascular disease has been proved to be a primary link between them which is supported by the vascular depression hypothesis 43,44. Evidence also indicates that ischemic damages to the brain, particularly the frontostriatal brain regions, might be a common etiologic factor for depression and cognitive dysfunction 38,45. Besides, it had been proposed that increased cortisone levels, frequently observed in depression, can lead to worsening hippocampal atrophy, which is a well-known characteristic of Alzheimer disease 38,46. Other possible systemic etiology includes chronic inflammatory processes 47 as well as changed levels of circulating brain-derived neurotrophic factors 48,49. Consequently, our study suggested that when implementing a screening program for the elderly outpatients, both dementia and depression should be included. What should be emphasized is that AD8 and BSRS-5 are not diagnostic tools. Further studies are needed to clarify the real mental status of those with positive results in both screening tools.
This study has some strengths. First, past studies have focused on screening for either dementia or geriatric depression, whereas ours is the first study to perform large-scale screening for both dementia and geriatric depression simultaneously. Second, our study targeted at-risk patients in the outpatient departments of medicine and surgery whose mental health are usually poorer but are ignored. Third, AD8 and BSRS-5 were used as screening tools, with the former capable of identifying even MCI and very mild cognitive impairment and the latter, being developed by the Taiwanese, have been used widely for more than ten years in Taiwan to screen depression which can minimize the culture bond. However, this study has several limitations. First, although the participants were volunteers, they were not recruited using randomized sampling from the outpatient department, which may have led to selection bias. Second, we did not separate the informant AD8 from participant AD8. Studies have suggested that the former could be more precise than the latter 50,51. Third, the elderly patients recruited were from only one hospital, which is in a cultural and educational district of Northern Taiwan. Furthermore, patients from our university hospital may have more complex comorbid illnesses than others do and cannot represent the general condition of elderly patients in the outpatient department. Fourth, we did not collect information regarding education and comorbidities of participants which contributed to the lacking of the content in descriptive statistics. Additionally, further evaluation for differential diagnosis was lacking, which made the analysis of sensitivity and specificity unavailable.
This study of implementing a screening program for both dementia and depression in a university hospital suggest the high ratio of, and significant overlap between, suspected dementia and suspected depression among the elderly outpatients. Given the projected increase in the dementia and geriatric depression population in the coming decades, large-scale screening of elderly adults may be needed for the early detection and early intervention of these two illnesses. Overall, this study strengthens the cost-effect of performing the screening in the elderly of outpatient department and the screening should include both dementia and depression. Further investigation should be conducted to elucidate the status of the cognition and emotion among the elderly outpatients especially those with both screening to be positive.