Citation

Plana-Ripoll O, Chen D, Laustsen LM, Momen NC. Lancet Psychiatry 2024; ePub(ePub): ePub.

Copyright

(Copyright © 2024, Elsevier Publishing)

DOI

10.1016/S2215-0366(24)00129-9

PMID

38642561

Abstract

Multimorbidity is common in those with mental illness, and further deterioration of mental health, reduced quality of life, and premature mortality have been reported in those with multiple disorders. 1 , 2 , 3 Given that comorbidity is often an exclusion criterion in intervention studies, 4 evidence from observational studies plays a crucial role in our understanding of its associations with health outcomes. The systematic review and meta-analysis presented by Sean Halstead and colleagues 5 provides estimates of multimorbidity (ie, the coexistence of two or more chronic physical conditions [physical multimorbidity] and the coexistence of three or more psychiatric disorders [psychiatric multimorbidity]) in those with schizophrenia-spectrum disorder and bipolar disorder. They report that 25% (95% CI 0·19–0·32) of individuals with these severe mental illnesses have physical multimorbidity, which represents 2·40 (95% CI 1·57–3·65, p=0·0009) times the prevalence in people without severe mental illness, highlighting the pervasiveness of multimorbidity in this population. Furthermore, the authors report that 14% (95% CI 0·08–0·23) of those living with schizophrenia-spectrum disorder and bipolar disorder experience psychiatric multimorbidity. Included studies were predominantly cross-sectional studies carried out in North America or Europe, with high heterogeneity (I2>90%). Based on this comprehensive review, we would like to point out several challenges that remain in the larger context of multimorbidity research. The concept of multimorbidity is extremely complex and arguably impractical to be fully captured in epidemiological research studies—a wide range of disorders; variation in the number, severity, and treatment of comorbidities; different dates of onset (and potentially recovery); and multiple pathways.

Thus, multimorbidity research requires simplification. Yet, it remains challenging to achieve simplicity without compromising on the comprehensiveness. The challenge is evident in the 82 studies included in the systematic review by Halstead and colleagues; 5 only four studies considered both physical and psychiatric multimorbidity. Limited definitions of multimorbidity are also seen more widely in the literature, as described by Skou and colleagues. 6 Researchers often consider disorder pairs, counts of conditions within a list, or weighted indices. The pitfalls of using counts and weighted indices have previously been highlighted, 7 including that researchers need to consider the populations and outcomes for which they were developed. Halstead and colleagues 5 found that, compared with those without severe mental illness, the prevalence of multimorbidity was 4 times higher (odds ratio [OR] 3·99, 95% CI 1·43–11·10) among individuals with severe mental illness younger than 40 years, but 1·5 times higher (OR 1·55, 95% CI 0·96–21) for those older than 40 years, indicating that relevant comorbid diseases are likely to differ by age. Well designed, thorough lists and indices can facilitate multimorbidity research through consideration of a variety of disorders, but the potential for interaction between psychiatric and physical disorders on associations should also be considered. 8 , 9 Depending on the nature of data, it might be possible for researchers to consider more complex patterns of comorbidity, as shown by Weye and colleagues

Language: en