Introduction
Stroke is the second most common cause of mortality globally and one of the highest contributors to disease burden in low- and middle-income countries.1 The prevalence of stroke increases dramatically with age, and the number of people living with stroke is rising with the ageing population worldwide.2 In the European Union, there were approximately 9.53 million stroke survivors in 2017, and the figure is expected to increase by 27% in the next 30 years.3 Critically, in China there were 28.76 million cases of stroke in 2019, according to the Global Burden of Disease Study.4 Additionally, stroke is the leading cause of chronic severe disabilities among adults, often resulting in substantial functional impairments and needing long-term rehabilitation across various phases of recovery.1 5 6 Thus, despite current advances in prevention and treatment, stroke remains a significant concern for both survivors and families, posing exceptional challenges to healthcare systems worldwide.7 8
Post-stroke depression (PSD), which is the development of a depressive disorder after a stroke, is considered to be one of the most prevalent and important causes of illness burden among all neuropsychiatric disorders.9 10 A meta-analysis of 61 studies covering 25 488 patients found that the pooled prevalence of PSD was 31% (95% confidence interval (CI) 28% to 35%) within a 5-year post-stroke period.11 Depression is found to be significantly associated with stroke,12 13 and the burden of both stroke and depression contributes to substantial loss of healthy life due to disability.14 PSD typically occurs within 3–6 months following a stroke, and the prevalence of PSD can be high even up to 3 years after a stroke,15 resulting in worse functional outcomes, poorer quality of life (QoL) and higher mortality among survivors.16–19 For instance, a cross-sectional analysis from the Stroke Data Bank (USA) showed that stroke survivors with depression experienced greater impairment in activities of daily living (ADL) compared with those without PSD.19 Additionally, a prospective survey found that QoL was significantly affected by PSD,17 and a systematic review showed that lower QoL was associated with PSD.18 Further, a meta-analysis including 119 075 individuals with stroke revealed a higher mortality in older adults with PSD compared with those without PSD (relative risk=1.50; 95% CI 1.28 to 1.75; p<0.001).16 A recent review grouped the risk factors of PSD into three categories: (1) pre-stroke (eg, female gender and family history of mental illness), (2) stroke-related (eg, location of the lesion) and (3) post-stroke (eg, first year after stroke, higher level of disability and social isolation).20 The most common risk factors found in PSD included stroke severity, cognitive dysfunction, physical impairment and functional dependency.21 Identifying these risk factors could help guide early identification of comorbid depressive symptoms and facilitate timely preventive interventions.20 In China, the average age of stroke survivors is around 65 years old, which is 10 years younger than that in developed countries.22 Among older stroke survivors in China, PSD not only has an adverse long-term impact on their QoL but also contributes to caregiver burden.23 Therefore, understanding the prevalence and correlates of depression among older Chinese stroke survivors is important to address the burden. However, to date, most previous studies have only examined PSD based on total or mean scores of standard scales such as the Hamilton Depression Rating Scale and Patient Health Questionnaire,24 25 even though depression comprises different symptoms. Hence, the exploration of the relationships between individual depressive symptoms has not been adequately assessed.
Network analysis is a novel approach to understanding the psychopathological structure and conceptualising psychiatric disorders (eg, depression).26 In contrast to traditional statistical methods (eg, regression analysis and factor analysis) which typically identify the effects of a latent disorder,27 the network approach provides a consistent and transparent theoretical framework to conceptualise a psychiatric disorder or syndrome as a system of connected symptoms that can be visualised, analysed and studied.26 Network theory suggests the potential for prioritising therapeutic targets by identifying central (influential) symptoms that are strongly connected to other symptoms within a network.26 28 Few studies on PSD have used a network approach, for example, in a network analysis using the Centre for Epidemiological Studies Depression Scale-20 (CESD-20) among US stroke survivors aged 65 and above, ‘sadness’, ‘blues’ and ‘depressed’ emerged as the most central depressive symptoms.27 In clinical practice, interventions for treating and/or decreasing a single central symptom might lead to the inhibition of symptom-to-symptom interactions and a reduction of overall network activation, which might eventually prevent the progression into a disorder.29 Hence, it is critical to conduct a network analysis to depict the network structure of depressive symptoms and identify the central symptoms.
Further, few studies have investigated the prevalence of PSD and its associated factors, as well as employing network analysis to explore the structure of depressive symptoms among older stroke survivors. Therefore, based on a national survey in China, the Chinese Longitudinal Healthy Longevity Survey (CLHLS), our study aimed to investigate the prevalence and correlates of PSD among Chinese older stroke survivors, the depressive network structure and central symptoms, and examine the correlation of individual depressive symptoms with QoL. We hypothesised that PSD would be common among older Chinese stroke survivors, while certain depressive symptoms, such as ‘feeling blue/depressed’ would be the most central symptom and negatively associated with QoL.