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SPECIAL SECTION |
1 Geriatrics Branch, Geriatrics and Clinical Gerontology Program, National Institute on Aging, Bethesda, Maryland.
2 Clinical Research Branch, National Institute on Aging, Baltimore, Maryland.
3 School of Public Health, University of California–Berkeley.
4 VA Puget Sound Health Care Systems, Seattle, Washington.
5 Center for the Study of Aging, Duke University Medical Center, Durham, North Carolina.
Address correspondence to Rosemary Yancik, PhD, National Institute on Aging, NIH, Geriatrics and Clinical Gerontology Program, 7201 Wisconsin Ave., Suite 3C307, Bethesda, MD 20892. E-mail: yancikr{at}nia.nih.gov
THE National Institute on Aging (NIA) Geriatrics and Clinical Gerontology (GCG) Program convened an interdisciplinary Task Force on Comorbidity to foster the development of a research agenda on the multiple concurrent health problems that often occur in older persons. This report summarizes Task Force discussions held in Bethesda, Maryland (October 21–22, 2003; July 20–21, 2004) and serves as an introduction to the following three articles that address specific issues such as the nosological classification of impairment for the construction of comorbidity measures, staging and classification of disease severity, and methodological and analytical issues.
The risk of developing concomitant chronic illnesses and physiological limitations escalates with aging. Diabetes, respiratory diseases, cancer, cardiovascular problems, arthritis, hypertension, and certain other chronic conditions are more common in older than in younger persons. As a consequence, a new diagnosis of any common chronic health condition is likely to be made in the context of preexisting health problems.
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INTRODUCTION |
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Some changes involving natural and pathologic processes of aging affect almost everyone who lives long enough. Arthritis, hypertension, cancer, diabetes, osteoporosis, and Alzheimer's disease occur primarily in older persons. Diseases of the cardiovascular, cerebrovascular, and pulmonary systems are other health conditions notably encountered in older individuals. Functional limitations, impairments, and geriatric syndromes (e.g., incontinence, falls, disability) are commonly associated with aging.
Certain pathological states are clinically evident and have a clear nosological definition; others remain subclinical (e.g., restricted reserve in organ systems) at least to a superficial investigation. In addition, a number of conditions typical of older persons clearly impact their health status (e.g., sarcopenia, anemia, chronic inflammation), but are not yet considered in the traditional disease nosology. Coexistence of these factors and the possibility of different interactions between or among them make evaluation of an older person's overall health status extremely challenging.
The health care needs and comorbid health problems of older Americans call for a special focus. Thus, the NIA GCG Program convened a task force of leaders in research on aging from different disciplines and professions (e.g., geriatrics, gerontology, social science, nursing, medical specialties, and epidemiology) to explore conceptual and methodological complexities of comorbidity and its assessment. Task Force on Comorbidity members and consultants are listed in the Appendix.
William R. Hazzard, MD, chaired Task Force Meeting I. Harvey Jay Cohen, MD, chaired Task Force Meeting II. William Ershler, MD, and William Satariano, PhD, chaired the two break-out groups convened within each Task Force on Comorbidity meeting. The groups were charged with two related tasks: to lay the groundwork for research on medical treatment in the context of multiple health conditions, and to identify the steps needed to translate the concept of comorbidity into clinical practice.
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TASK FORCE OBJECTIVES |
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A synthesis of various perspectives expressed in the two Task Force meetings is provided in this report. Three NIA-commissioned background articles for Task Force discussions appear in this issue of the Journal.
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CONCEPT EXPLORATION |
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There was consensus that more focus on comorbidity is needed both in geriatric care and in clinical research on aging. The development of specific assessment tools is necessary to drive research and clinical care aimed at improving prognosis, diagnosis, treatment, and care of older persons with multiple health conditions. Yet the need for advancing conceptual and theoretical aspects of comorbidity should not be hampered by excessive simplification and operationalization—otherwise, there is a risk of losing sight of the real and practical issues.
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IT DEPENDS ON THE QUESTION |
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Comorbidity indicates the co-occurrence of preexisting age-related health conditions (e.g., disability, anemia, impairments, urinary incontinence) or diseases (e.g., diabetes, heart disease, hypertension) in reference to an index disease (e.g., cancer, Parkinson's disease, diabetes). On the other hand, multimorbidity is the co-occurrence of two or more diseases or active health conditions (e.g., aggregate of coequals) that may or may not be linked by a causal relationship or with no consistent dominant index disorder.
The full scope of assessing multimorbidity is currently a matter of debate. It could include a range of complex health problems and also embrace conditions such as impairment, disability, and physiological levels, alone or in some combination. Combining a mixture of diseases and conditions of variable severity, functional processes, and biological processes under a single term is quite complicated. Therefore, measuring multimorbidity may be intrinsically more difficult than concentrating on comorbidity.
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RESEARCH APPROACHES/FRAMEWORKS |
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SECOND CONDITIONS |
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There is a clear trade-off between the need for a standard, dichotomous definition for disease and the progressive and interacting nature of diseases. The clear-cut criteria play an important role in guiding clinicians' ability to cure patients affected by single diseases and to predict effects of specific interventions. In the geriatric experience, however, it is becoming clear that the health status of older individuals is affected by the accumulation of biological dysfunctions in multiple systems. Each one may contribute to the clinical picture, even those whose severity is not yet over a diagnostic threshold for the standard definition of a disease. For example, borderline value of blood markers may become important predictors of outcome in older persons with substantial comorbidity.
Dr. Jeanne Mandelblatt (Figure 1) proposed that research on comorbidity should consider subclinical and mechanistic approaches as two separate, but complementary pathways. In parallel, comorbidity indices should be developed to address specific outcomes (e.g., mortality, quality of life, disability, health care utilization). In this framework, one may look at comorbidity in each of the different areas to identify appropriate tools to measure overall aspects of health status that are relevant domains. Dr. Mandelblatt's schema provides an overview of research complexity and issues. For example, on a continuum from risk factor to preclinical disease to overt disease, elements essential in a measure of multiple morbidities depend upon the nature of the research question.
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An inclusive biomedical framework of age-related issues that a practitioner or clinical researcher faces was presented by Dr. Evan Hadley (Table 1).
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MEASURES OF COMORBIDITY AND MULTIMORBIDITY ASSESSMENT |
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Selection of measurement tools for health appraisal varies according to the setting, population, and research questions. A challenging aspect in using summary measures of comorbidity concerns how to categorize and determine influence of particular combinations of conditions. Indeed, summary measures may impede progress in understanding issues of sequencing, the impact of sequencing, and nonlinearity. Current measures and methods, diverse in content and approaches, have different outcome goals and are limited in prognostic perspective. They include interviews, self-reports, medical record reviews, death certificates, administrative and medical record databases, summary indices derived from presence of selected conditions, and, less frequently, observations of physical functioning of patients. Combined effects of the comorbid conditions are not often determined. Indices that do approach the relationship between and among conditions are limited.
Relative to comorbidity and multimorbidity indicators, three measurement issues were cited: 1) Limitations in functional status. The degree of independence or difficulty in basic and instrumental activities of daily living should be considered for inclusion in all comorbidity evaluations. 2) Severity levels of comorbidity and multimorbidity should address additive and multiplicative relationships. 3) Although biologic and physical responses within individuals are major foci of treatment and care, they are not disconnected from social and psychological events and changes occurring in older patients' lives.
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SUMMARY OF CENTRAL ISSUES |
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The critical question is how best to utilize and apply the multilayered systems of information (e.g., on diseases, other health conditions, impairments, functioning, or disabilities) on behalf of older persons. Table 2 outlines issues that warrant further conceptual clarification and progress to improve prevention, earlier detection, prognosis benefit, and treatment decisions of health conditions typical of olderpatients.
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Appendix |
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Harvey Jay Cohen, MD
Duke University Medical Center, Durham, NC
William Ershler, MD
NIA Intramural Program, Baltimore MD
Institute for Advanced Studies in Aging and Geriatric Medicine, Washington, DC
Martine Extermann, MD
University of South Florida, Tampa, FL
Luigi Ferrucci, MD
NIA Intramural Program, Baltimore, MD
Linda Fried, MD
Cynthia Boyd, MD (Consultant)
Johns Hopkins Medical Institutions, Baltimore, MD
Jerry H. Gurwitz, MD
Meyers Primary Care Institute, Worcester, MA
Jeffrey Halter, MD
University of Michigan, Ann Arbor, MI
William R. Hazzard, MD
VA Puget Sound Health Care Systems, Seattle, WA
Carrie Klabunde, PhD
National Cancer Institute, NIH, Bethesda, MD
Jeanne S. Mandelblatt, MD, MPH
Georgetown University Medical Center, Washington
Vincent Mor, PhD
Brown University, Providence, RI
Marco Pahor, MD
University of Florida, Gainesville, FL
David Reuben, MD
Arun Karlamangla, MD (Consultant)
University of California, Los Angeles, CA
William Satariano, PhD
University of California at Berkeley, CA
Rebecca Silliman, MD, PhD
Timothy Lash, DPH (Consultant)
Boston Medical Center, Boston, MA
Stephanie Studenski, MD
University of Pittsburgh, Pittsburgh, PA
Mary Tinetti, MD
Yale University School of Medicine, New Haven, CT
Claudette G. Varricchio, DSN, RN
National Institute of Nursing Research, NIH
Terrie Wetle, PhD
Brown University, Providence, RI
Darryl Wieland, PhD, MPH
Palmetto Richland Memorial Hospital, Columbia, SC
National Institute on Aging Staff
Jack Guralnik, MD, PhD (NIA Intramural Program)
Evan Hadley, MD
J. Taylor Harden, PhD, RN
Susan Molchan, MD
Susan Nayfield, MD
Rosemary Yancik, PhD
National Institutes of Health, Bethesda, MD
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The NIA is grateful for the outstanding leadership provided by Dr. William Hazzard and Dr. Harvey J. Cohen, who chaired Task Force Meetings I and II, respectively. The resourceful assistance of Dr. William Ershler and Dr. William Satariano is appreciated for their leadership and effective guidance as chairpersons of the two Task Force break-out groups in both meetings.
The authors are pleased to acknowledge Dr. Jeanne Mandelblatt's comprehensive conceptual contribution displayed in Figure 1, Dr. Luigi Ferrucci's rendition of "a common sense" paradigm in Figure 2, and Dr. Evan Hadley's biomedical framework of age-related issues in Table 1.
The Task Force research recommendations in Table 2 and potential lines of inquiry in Table 3 emphasize interdisciplinary approaches reflecting the make-up of the NIA Task Force on comorbidity itself. We are grateful for the many thoughtful suggestions and issues raised by the participants. Special thanks to the Study Team efforts that resulted in the three background articles included in this issue.
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Received August 11, 2006
Accepted January 12, 2007
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References |
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Introduction
Task Force Objectives
