Chronic disease management is usually based on evidence from trials of single conditions. Literature shows little evidence of research specifically addressing multimorbidity in the primary care setting, as most individuals with multimorbidity are excluded from studies to minimise bias, even though these patients are the most frequent attenders in primary care. In other cases, comorbidities are frequently not reported in research participants.
Most studies in the area are epidemiological in design (thus demonstrating that multimorbidity is a growing concern) rather than healthcare outcome-based. Whilst this may help identify prevalence, many do not take into account the disease burden, or examine interventions for improving outcomes.
The first difficulty researching multimorbidity is a lack of a consistent definition. It isn’t a MeSH term, so needs to be entered as a keyword when doing database searches, further compounded by its use interchangeably with the term ‘comorbidity’. Fortin et al recommend ‘multimorbidity’ be added to the database thesaurus to make literature reviews on this topic more effective.
In addition, the WHO’s definition of chronic disease covers a huge number of conditions. Selection of disease combinations differ, as do the number of diseases they count as multimorbidity (some as two or more diseases, whereas others require three plus). Furthermore, researchers and healthcare professionals differ in their view on what is a chronic disease, for example, some see lipid lowering medication as risk factor management rather than chronic disease management. All this makes comparison and generalization difficult.
Patients with multimorbidity report the poorest level of Health Related QOL (HRQOL). Simple disease-count has a weak correlation with HRQOL. Additional variables such as perceived social support, age, education, perceived economic status and residual Cumulative Illness Rating Scale (CIRS) need to be taken into account. These factors further complicate researching multimorbidty.
In summary, the complexity of multimorbidity in its definition, identification, severity, burden, confounding variables, and the difficulty in examining outcomes simultaneously and on a multiple basis, in any one individual, combine to make researching multimorbidity a challenge. However, Fortin et al are representative in their thinking that “it is essential to increase primary care research into multimorbidity, in order to develop a better understanding of this important topic”. The International Research Community on Multimorbidity (IRCMo) has been established to address this http://pages.usherbrooke.ca/crmcspl-blog/