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14-01-2014 | Comorbidities | Article

Multimorbidity and rheumatic conditions—enhancing the concept of comorbidity

Helga Radner, Kazuki Yoshida, Josef S Smolen, Daniel H Solomon


The concept of multimorbidity is still poorly understood and not well integrated into medical care and research. For clinicians involved in rheumatology care for an ageing patient population who have multiple diseases, multimorbidity is the rule not the exception. The interaction of different diseases and the impact they have on important clinical outcomes, such as physical function, quality of life and mortality, should all be considered by the rheumatologist. Treatment decisions must be adapted for the patient with multimorbidity to best serve the individual and society. This Perspectives article describes the concept of multimorbidity, how it differs from comorbidity, and outlines why an increased understanding of multimorbiditiy will enhance our overall clinical practice and research focus.

Nat Rev Rheumatol 2015;10:252–256. doi:10.1038/nrrheum.2013.212

In the past 15 years, clinical and research interest in comorbidities and multimorbidities have increased.1, 2, 3, 4, 5 However, in the published literature the terms comorbidity and multimorbidity are frequently, and confusingly, used interchangeably.6 A widely accepted definition of comorbidity is “the existence or occurrence of any distinct additional entity during the clinical course of a patient who has the index disease under study”.7 Rheumatic diseases are often systemic and special attention has, therefore, focused on coexisting diseases in the rheumatology patient. Several researchers have reported a high number of comorbidities in patients with rheumatic diseases. The average patient with rheumatoid arthritis (RA) patients has 1.6 comorbid conditions, and the number of these conditions increases with age, disease duration and/or disease activity.8, 9, 10 In populations of patients with RA in Germany, the longer the duration of RA (rather than older age) led to a more frequent occurrence of concomitant morbidities, such as cardiovascular disease, chronic renal disease or osteoporosis.11 Furthermore, comorbidities have a negative impact on patients' health, as they reduce function and work productivity, decrease quality of life, and might shorten life expectancy.9, 12, 13, 14, 15, 16, 17 In contrast to comorbidity, multimorbidity is poorly understood and an appreciation of this concept is not well integrated into care and research. However, in an ageing population with rheumatic diseases, multimorbidity is far more common, and might be viewed as the rule not the exception.18, 19, 20 This Perspectives article reviews the conceptual differences between comorbidity and multimorbidity, underlines the importance of multimorbidity in a clinical context, and discusses how it might impact care and research in rheumatology.

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