Comorbidity versus multimorbidity: Why it matters

The ‘Journal of Comorbidity’ is changing its name to the ‘Journal of Multimorbidity and Comorbidity’. This may seem redundant, as many see ‘comorbidity’ and ‘multimorbidity’ as interchangeable terms. We believe it is important to highlight the distinction given the differences in how healthcare systems view patients with multiple chronic conditions (MCCs), and the important differences that arise in research and intervention development for these patients. In 1970, Feinstein first coined the term ‘comorbidity’ to describe ‘Any distinct additional entity that has existed or may occur during the clinical course of a patient who has the index disease under study’. From 1976, the term ‘multimorbidity’ was increasingly used by health researchers to describe patients with MCCs. Due to the growing ambiguity around the use of the terms comorbidity and multimorbidity, in 1996 van den Akker et al. suggested clear definitions for both terms. They suggested that comorbidity be defined according to Feinstein’s original definition and multimorbidity be defined as ‘the cooccurrence of multiple chronic or acute diseases and medical conditions within one person’. In 2010, Boyd and Fortin provided a simpler definition of multimorbidity: ‘the co-existence of two or more chronic conditions, where one is not necessarily more central than the others’.