COPD, Co-morbidities and Health-Related Quality of Life (HRQOL): More is Less

COPD is a complex disease that affects primarily the lungs but is frequently associated with non-pulmonary manifestations that impact the patient's health status and survival (1). COPD symptomatology typically manifests in the sixth decade of life, and other chronic and degenerative diseases may coexist with COPD either through the relationship with tobacco or environmental exposure, aging or particular predisposition. The concept that a co-morbidity is the presence of one or more distinct disorders that are not part of the spectrum of the natural history of COPD is evolving as we recognize that COPD is a systemic disease affecting other organ systems (2).

The identification and quantification of COPD related co-morbidities has gained relevance and practice guidelines recognize their importance in their most recent recommendations (3). Studies that have systematically explored COPD-related co-morbidities suggest that they impact outcomes such as health related quality of life (4,5), utilization of health care resources (6), response to pulmonary rehabilitation (5) and mortality (7).

In this volume of the Journal of Chronic Obstructive Pulmonary Disease, Dr. Putcha et al. describe the relationship between self-reported co-morbidities and quality of life in 843 individuals with self-reported diagnosis of COPD. The data set used is selected from the National Health and Examination Survey (NHANES), a program initiated in 1999, of 5,000 individuals representing the U.S. population selected for a comprehensive interview and a yearly examination including physiologic measurements, basic laboratory exams and spirometry. The NHANES data is available not only to governmental institutions but also for investigators at large.

In their analysis Dr. Putcha and her team found that those individuals with self reported diagnosis of COPD report a higher number of concurrent chronic conditions compared to sex-age matched counterparts. They also “dissected” the burden of co-morbidities by analyzing the additive effect of co-morbidities, the individual contribution of each disease and their prevalence on self-rated quality of life (QOL). They observed an inverse relationship between the number of co-morbidities and the perceived quality of life, where more co-morbidities in an individual is associated with less QOL. Using logistic regression models, they estimated the contribution of individual co-morbidities to QOL. In this analysis a handful of prevalent co-morbidities—namely congestive heart failure, diabetes mellitus, coronary heart disease, arthritis, asthma, urinary incontinence/prostate disease, depressive symptoms and obesity—were particularly more detrimental to self-reported QOL when combined with COPD.

Although the contribution by Dr. Putcha and her team help fill in the pieces of the COPD-co-morbidity puzzle, there are several limitations in their study, which the authors clearly note in their discussion. First, the use of self-reported COPD diagnosis and the lack of spirometric confirmation in this report limit specificity (and may lead to misclassification bias). Second, it remains difficult to weight the individual contribution of COPD severity and each co-morbidity on QOL a distinction that could impact treatment priority and management.

In fact, van Manen et al. (4) described a decade ago their analysis of the contribution of COPD severity versus co-morbidities and their influence on HRQOL (using the SF-36 questionnaire). In their study the authors described that physical functioning, vitality, and general health domains are largely impacted to COPD and to some extent to co-morbidity, while impairments in social and emotional functioning do not seem to be related to COPD, but only to co-morbidity. Third, the co-morbidities included in the NHANES survey, although important and prevalent in the general population, may have excluded important co-morbidities influencing outcomes in COPD, namely gastroesophageal reflux, duodenal ulcers, anxiety, pulmonary fibrosis and atrial fibrilation (7–9).

Perhaps the greatest value of this study is that it represents the perspective of the patients and provides information about their perception of disease burden. These findings should encourage clinicians to more carefully explore the presence of co-morbidities during patient history taking and interviews as an aid to understanding why some patients may not respond to standard respiratory treatment or rehabilitation (5) or why they are at higher risk for frequent hospital admissions. In our roles as specialists caring for COPD patients, this article should also remind us that we have to understand our patients in a more holistic manner.

As researchers, these results confirm the co-existence of diseases with distinct clinical /organ system involvement that may not be the result of pure chance, suggesting that perhaps there is some intermediate commonality in their origin, a fascinating connection that requires further exploration.