Studying trajectories of multimorbidity: a systematic scoping review of longitudinal approaches and evidence

Abstract

ABSTRACTObjectivesMultimorbidity – the co-occurrence of at least two chronic diseases in an individual-is an important public health challenge in ageing societies. The vast majority of multimorbidity research takes a cross-sectional approach, but longitudinal approaches to understanding multimorbidity are an emerging research area, being encouraged by multiple funders. To support development in this research area, the aim of this study is to scope the methodological approaches and substantive findings of studies which have investigated longitudinal multimorbidity trajectories.DesignWe conducted a systematic search for relevant studies in four online databases (Medline, Scopus, Web of Science, and Embase) using pre-defined search terms and inclusion and exclusion criteria. The search was complemented by searching reference lists of relevant papers. From the selected studies we systematically extracted data on study methodology and findings, and summarised them in a narrative synthesis.ResultsWe identified 34 studies investigating multimorbidity longitudinally, all published in the last decade, and predominantly in high-income countries from the Global North. Longitudinal approaches employed included constructing change variables, multilevel regression analysis (e.g. growth curve modelling), longitudinal group-based methodologies (e.g. latent class modelling), analysing disease transitions, and visualisation techniques. Commonly identified risk factors for multimorbidity onset and progression were older age, higher socio-economic and area-level deprivation, overweight, and poorer health behaviours.ConclusionThe nascent research area employs a diverse range of longitudinal approaches that characterize accumulation and disease combinations, and to a lesser extent disease sequencing and progression. Gaps include understanding the long-term, life course determinants of different multimorbidity trajectories, and doing so in across diverse populations, including those from low and middle-income countries. This can provide a detailed picture of morbidity development, with important implications from a clinical and intervention perspective.STRENGTHS AND LIMITATIONS OF THE STUDYThis is the first systematic review to focus on studies that take a longitudinal, rather than cross-sectional, approach to multimorbidity.Systematic searches of online academic databases were performed using pre-defined search terms, as well as searching of reference lists, and this is reported using PRISMA guidelines.For selected papers, data was double extracted using standardised proformas to aid narrative synthesis.Due to the heterogeneity of the studies included, their weaknesses were described in the narrative synthesis, but we did not perform quality assessment using standardised tools.