Evolution from pseudodementia to dementia: is depressive symptom an optional extra?

A growing interest in pseudodementia sheds light on further explorations of the underlying mechanism on the progress of cognitive impairment and subsequent development of dementia. Pseudodementia is defined as cognitive dysfunction co-occurring with depression, with especially high prevalence in older adults (Yaffe et al., 1999). Extant literature has noted that pseudodementia acts as a prodromal stage leading to dementia, frequently related to an increased risk of cognitive impairment (Alexopoulos et al., 1993; Sáez-Fonseca et al., 2007; Sohrabi et al., 2019). Featured by detectable, treatable, and preventable, intervention on pseudodementia may provide a window for earlier diagnosis and slower deterioration of the insidious dementia. Though a bunch of studies have been dedicated to exploring the relationship between geriatric depression and cognitive impairment, in the presence or absence of cognitive dysfunction, there is still a far way to reach the agreement on the association between these three disorders. Statically significant association between cognitive difficulties and cognitive impairment (Jessen et al., 2014; Reisberg et al., 2010), and between geriatric depression and cognitive impairment (Kang et al., 2014; Ownby et al., 2006) have been described in recent literature, yet no significant results also have been reported in several community-based cohort studies (Becker et al., 2009; Ganguli et al., 2006). Moreover, longterm indifference to older adults suffering cognitive dysfunction combined with depression can be proportionally attributed to this unsolved relationship, since they are considered as “not really dementia”, which is beyond the clinical threshold. Therefore, it is in great need to detangle the underlying mechanism wherein pseudodementia deteriorates to dementia on the perspective of depression, for maximizing the likelihood of a preventive strategy for dementia. A well-designed prospective large cohort focusing on community-based elder population would be a robust comparison to former researches. In this issue of International Psychogeriatrics, Shin (2020) provided novel insights into the geriatric depressive symptoms to test its relationship with the 12-year later cognitive impairment, in the presence or absence of cognitive dysfunction. The author hypothesized that depressive symptoms might have a long-term impact on future cognitive impairment among community-dwelling older adults, and this adverse situation accompanied by cognitive dysfunction would result in a significant increase in the development of dementia. The study was based on the Korean Longitudinal Study of Aging (KLoSA), a nationwide longitudinal panel cohort in South Korea, focusing on a total of 10,254 community-dwelling older adults aged 45 years or older. Shin examined 4547 individuals in the cohort who were free from depressive symptoms and cognitive dysfunction at baseline (the first wave conducted in 2006), completing up to seventh wave by 2018. To clarify the individual impact and joint effort of depressive symptoms and cognitive dysfunction on cognitive impairment, four groups were subdivided using the CES-D10 Scale, a 10-item short-form version of the Center for Epidemiological Studies-Depression Scale (Andresen et al., 1994), and the K-MMSE, a Korean version of the Mini-Mental State Examination (Kang et al., 1997), respectively. To highlight, four stable groups were reclassified depending on whether the depressive condition and cognitive status of each individual remained in the same category at the second and third waves. If so, they would be deemed as stable. A comparison of survival curves between original and stable grouping was then performed aiming at adjusting the potential influence of short-term exposure fluctuations on the key event. The point of Shin’s study was the hazard calculation of four exposure groups in the contest of survival analysis. The pseudodementia group experienced the highest hazard ratio and the severest loss of survival, suggesting that depressive symptoms accompanied by cognitive dysfunction play a significant role in predicting long-term cognitive impairment. Nonetheless, older adults subject to depressive symptoms while free from cognitive dysfunction reported no significant difference in terminal events compared with the control group. Therefore, this study drew a conclusion that depressive symptoms co-occurred with cognitive dysfunction did pose threats to long-term cognitive impairment, even though depressive symptoms alone demonstrated no significant causal effect. International Psychogeriatrics (2021), 33:8, 751–754 © International Psychogeriatric Association 2021