Making meaning of multimorbidity and severe mental illness: A viewpoint

Abstract

People living with severe mental illness, such as schizophrenia and bipolar affective disorder, frequently experience poorer physical health compared to those without mental illness. This issue has hitherto been approached through the disease-centred construct of comorbidity, where subsequent conditions are viewed as secondary to an ‘index condition’. In contrast, this Viewpoint sets out to explain why multimorbidity, a patient-centred concept that instead refers to the coexistence of multiple chronic illnesses, is a more versatile and robust framework for tackling the issue of poor physical health in people with severe mental illness. In establishing this argument, this Viewpoint has sought to address three key areas. First, this article will discuss the epidemiology of both physical and psychiatric multimorbidity, with respect to how they manifest at greater frequency and at younger ages in people with severe mental illness. Second, the profound consequences of this multimorbidity burden will be explored, with respect to the ‘three D’ s’ of death (premature mortality), disability (functional impacts) and deficit (health-economic impacts). Finally, the utility of multimorbidity as a framework will be illustrated through a proposal for a three-dimensional multimorbidity construct composed of (1) quantity, (2) severity and (3) duration of an individual’s chronic illnesses. Consequently, this Viewpoint aims to capture why it is necessary for modern psychiatry to grasp the concept of multimorbidity to facilitate holistic healthcare for people living with severe mental illness.

Physical multimorbidity and mental illness: A global challenge

“…The latter enables a more comprehensive recognition of the multitude of permutations of chronic physical diseases that people with severe mental illness can experience. Multimorbidity is not a static risk factor that is either present or absent; rather, it is a dynamic variable that is best accounted for by capturing not only all the physical conditions an individual has, but also the years they have lived with each of them at their respective levels of severity (Halstead et al., 2023). Contextualising the cumulative exposure to chronic physical disease that people with severe mental illness experience enables identification of where prevention and management strategies will have the most impact.…”

“…Now, over 50 years later, the idea that the most vulnerable populations are often those with the worst access to safe and quality health care regrettably remains an established reality for a multitude of public health issues. While advances in public health and medicine have otherwise facilitated many gains in population health outcomes, the inverse care law remains particularly apparent in the stark health inequities faced by people living with severe mental illness, highlighted by the significantly reduced life expectancy and increased burden of disability faced by this cohort globally (Halstead et al., 2023).…”

“…A key driver behind these health inequities is the concomitant poor physical health experienced by people living with severe mental illness. Historically, this physical health disparity has been viewed through the lens of comorbidity , a reductionist construct built around disease pairs, where additional health conditions, such as type 2 diabetes mellitus, are classified as being secondary in clinical importance to an index condition, such as schizophrenia (Halstead et al., 2023). Multimorbidity , by contrast, is an emerging term defined as the simultaneous presence of two or more long-term conditions in an individual.…”

“…The advantage of the term multimorbidity is that it allows for better recognition of the cumulative effects of multiple chronic illnesses, rather than supporting a view of each comorbidity representing an isolated entity that is secondary to an index disease. Physical multimorbidity specifically refers to the presence of multiple chronic physical conditions, which facilitates a framework useful for characterising the physical health deficits of people with severe mental illness (Halstead et al., 2023).…”

“…This is further compounded when polypharmacy occurs where an individual is prescribed multiple concurrent psychiatric medications without clinical rationalisation. Exposure to physical multimorbidity at significantly younger ages amounts to a greater lifetime exposure risk to chronic physical disease; we previously hypothesised that this increased longitudinal exposure to chronic disease contributes to the poorer health outcomes faced by those living with severe mental illness, such as premature mortality and increased rates of disability, not to mention significantly greater health economic impacts (Halstead et al., 2023).…”