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Br J Gen Pract. 2007 April 1; 57(537): 268–270.
PMCID: PMC2043326

Chronic diseases: what happens when they come in multiples?

Susan M Smith
Trinity College Dublin, Department of Public Health and Primary Care

Multimorbidity is the coexistence of two or more chronic diseases in an individual.1 Prevalence studies indicate that it is the normal state of affairs, especially in patients over the age of 65 years.1 A smaller sub-group of patients are more severely affected by multimorbidity as the combination and severity of their conditions results in significant loss of function, poor quality of life, and frequent hospital admissions. There is a need to examine the health care of patients with multimorbidity, as they often receive fragmented specialist care which does not meet their needs, or indeed support their professional carers, especially in primary care.

Chronic disease care is now based on protocol driven management for a single disease across primary and secondary care.2 The commonly used term ‘comorbidity’ implies that there is an index disease to which coexistent diseases relate and may share an aetiology and perhaps a solution. In clinical practice individual patients often suffer from a collection of chronic illnesses which may or may not have a common aetiology, but which require greatly differing and often incompatible management. This is why we use the term multimorbidity here.

Individuals with multimorbidity are more likely to die prematurely, be admitted to hospital, have longer hospital stays, poorer quality of life, and a loss of physical functioning.3,4 They are more likely to suffer from depression, to be receiving multiple medications, and to have consequent difficulties with adherence to treatment and polypharmacy.5,6 Qualitative research indicates that patients with multimorbidity identify loss of function and polypharmacy as key problem areas.7 There are multiple barriers to self-care including physical limitations and aggravation of one condition by treatment of another.8 Research also highlights difficulties accessing care8 and problems with healthcare providers, particularly specialists.7 Analysis of data from the Quebec Health Survey indicated that patients with more than one chronic condition were significantly more likely to have higher levels of psychological distress and poorer mental health.9

The full physical and psychological impact of multimorbidity depends on the disease combinations, severity of coexisting conditions, and the age of the patient. Multimorbidity has knock-on effects for family members who face dependency issues and social isolation. While support may be available from voluntary organisations for single diseases, it is less likely to be available for multimorbidity. The result can be a housebound patient disabled by a number of illnesses receiving low level primary care and some social support in a therapeutically inconclusive manner.

Difficulties in management result in frequent emergency hospital admissions and repeated investigations with costs for both individuals and the healthcare system. A UK report has highlighted the costs associated with this group of patients who are described as ‘high impact users’ on the basis of their frequent emergency admissions.10 The 15% of people with three or more chronic conditions account for almost 30% of inpatient days in the UK.11

Disease specific protocols are probably best suited to younger patients with single conditions who have not yet developed other diseases. However, for the majority of patients such guidelines may be clinically naïve, in that they fail to take account of the reality of multimorbidity in an increasing number of patients. A study of US adults with at least one of five common chronic conditions (diabetes, ischaemic heart disease, hypertension, asthma, and mood disorder) indicated that 60%; of patients with ischaemic heart disease and 55% of patients with diabetes had at least one of the other conditions. This may affect how clinical guidelines for each condition can be implemented and has led to12 more generic approaches to chronic disease management, such as the Chronic Care Model in the US.13 It is designed to enhance coordination of care for people with chronic disease and focuses on four concurrent strategies: self-management support; practice teams to achieve clinical and behavioural management; disease support; and clinical information systems.14 Even this model may struggle with multimorbidity as its decision-support component relies on research evidence that is largely derived from studies of single diseases or conditions. Little research is available for multiple coexisting conditions, as individuals with multimorbidity are often excluded from such studies to minimise bias.15 Unless specifically designed to do so, clinical information systems may fail to support multimorbidity management if they do not pay sufficient attention to outcomes of function, which may be the main concern for the patient. In addition, financial incentives in disease management programmes may encourage a focus on individuals with single chronic conditions, who may be easier to manage to achieve predefined targets.

Further interventions have been developed to address multimorbidity. These include the programme for community matrons in the UK, delivered through primary care trusts and based on nurse-provided case management.16 It is similar to previous programmes delivered through social services in the 1990s. However, concerns have been expressed about achieving programme targets without real integration of primary and specialist services, and it has has also been claimed that community matrons may lack the necessary power and resources to improve outcomes.17 Disappointingly, a recent evaluation of community matrons working within the EverCare model, designed to reduce admission in frail older people, found that while the quality of care improved there was no reduction in emergency admissions or mortality.18

Research on multimorbidity has been limited and has focused on describing prevalence, estimating severity,19 and quality of life measures.4,20,21 Any future research must include the effectiveness of single disease guidelines in patients with multimorbidity. We have yet to explore the natural history of patients with multimorbidity, which at present seems to represent the limits of the healthcare system rather than a realistic response to a common, but complex, series of health problems. So far, there has been limited research into the effectiveness of interventions to improve outcomes in patients with multimorbidity19 leading to a weak scientific basis for patient management.

Clinical care of patients with multimorbidity is compounded by poor communication between primary and secondary care. Evidence from the US suggests that patients with a high morbidity burden have a higher use of specialists, even for conditions that are normally managed in primary care,22 and that care in both sectors is poorly integrated.14 A function-oriented approach, as opposed to a disease-oriented approach, is probably better suited to such patients. By this we mean a focus on whether a patient can function in a way that they find acceptable, as opposed to whether they have achieved a disease-related target such as blood pressure reduction. Their management requires complex clinical decision making, particularly in relation to polypharmacy,5 and understanding and minimisation of potential harm associated with multiple high-tech interventions. To address these issues properly requires clinical training with a philosophy that balances good medicine, pragmatism, and a consideration of quality of life and function. Given the complexity in making diagnoses and choosing treatments it seems that a broadly-trained generalist with a good breadth of knowledge and extra time is essential. A generalist needs the backup of a multidisciplinary team to improve function and care within the home or community. A review of coordination of care for chronic diseases in the US has highlighted the key roles of the generalist physician in coordinating care and also the role of the multidisciplinary team in integrating community and social services into the care plan.23 It is evident that such patients will need to attract additional resources for the time needed to deal with complex problems.

Traditionally, specialists have managed patients with complex chronic disease referred to them by generalists. In the US, Gask has highlighted the potential of changing specialist roles in chronic disease care by moving to stepped-care programmes, such as those developed for depression.24 These innovative approaches, which increase patient access to specialist expertise, are also based on single conditions but could be extended to patients with multimorbidity. Specialist physicians embedded in the multidisciplinary team, such as those looking after older people, may be in a position to support the management of multimorbidity patients in primary care. Other models may be more appropriate in different healthcare systems depending on the ability of primary care to deliver and the extent of sub-specialisation at the secondary and tertiary care levels. It would be inappropriate to adopt models of care reported in other healthcare systems without sufficient consideration of relevant contextual factors.25 Whatever way care for patients with multimorbidity is organised, there needs to be a shift towards a focus on function and quality-of-life-based care as prioritised by the individuals with multimorbidity themselves. A focus on functional status rather than disease-specific outcome measures will enable assessment of response to treatment in clinical practice, but will also be more appropriate in terms of research outcomes.

Multimorbidity is generally a consequence of increased longevity and better health care. However, as it is currently approached it represents the limits of the very health care that has contributed to its existence. There has been a discussion on the rising global challenge of the chronic disease epidemic.26 Innovations to address this challenge will need to incorporate a consideration of multimorbidity and move beyond a focus on a collection of single chronic conditions. New approaches will need to recognise the existence and complexity of multimorbidity if we are to provide balanced pragmatic and cost-effective care and address the expectations of both patients and healthcare providers.


We would like to acknowledge and thank Professor David Mant, Professor Bernard Walsh, Professor Fergus O'Kelly, Dr Jim McShane, and Ms Deirdre Handy for helpful comments regarding earlier drafts of this paper.


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