Co-morbid disease in COPD – more than a coincidence

Chronic obstructive pulmonary disease (COPD) is a major cause of disability and death worldwide. Its prevalence and mortality are increasing disproportionately among the elderly, women, persons of lower socioeconomic status, and the populations of developing countries (Anthonisen 1988; Borson et al 1998; Andreassen and Vestbo 2003). There is increasing recognition that COPD is a complex disorder, with many associated co-morbidities. The term “co-morbid” has traditionally been interpreted as “a medical condition existing simultaneously but independently with another condition in a patient.” However, this does not seem to fit the more recent research on patients with COPD as co-morbid conditions occur more frequently in these patients that would be expected by chance. Such conditions include cardiovascular disease (CVD) (Calverley and Scott 2006), depression (Borson et al 1998), diabetes (Schmidt et al 1999), lung cancer (Omori et al 2006), and osteoporosis (Vogelmeier and Bals 2007). Some of these conditions may be worsened by COPD or complicated by COPD. For instance raised airway glucose concentrations in the airways that may occur in diabetes have been shown to precede an increase of respiratory pathogens (Baker et al 2006) and cardiovascular disease (CVD) is a very common cause of death in patients with COPD (Calverley and Scott 2006).

The paper by Anecchino and colleagues (2007) in this issue adds to the literature on the prevalence of co-morbidities in patients with COPD reporting on a study of the prevalence of COPD and 3 treated co-morbidities: CVD, depression and osteoporosis in Italy. This is an important study as it utilizes data from a large cohort of approximately 123,000 possible COPD patients. Of note is the high proportion (98%) of these patients who had been prescribed at least one “nonrespiratory” drug.

We need however to be cautious in interpreting this data for a number of reasons. Patients in this study were defined as having COPD and the co-morbid conditions by drug treatment rather than having a specific diagnosis. This means the patients studied may have had other respiratory diseases such as asthma and that patients with untreated CVD, depression and osteoporosis are excluded. Unfortunately, the authors chose to report on just three specific co-morbidities, cardiovascular, diabetes and depression. It is hoped that the authors will go on to include other important co-morbidities such as osteoporosis.

There appear to be a number of mechanisms by which co-morbid conditions arise in patients with COPD other than by chance. The first of these is sharing of common risk factors. These include poor socioeconomic status, smoking and age which are clearly risk factor for a large range of conditions. Indeed half of all people aged 65 years or older have been reported to have at least three chronic medical conditions, and a fifth have five or more (Boyd et al 2005). Another mechanism is the increasingly well described systemic effects of COPD (Fabbri and Rabe 2007). This systemic inflammation is now thought to impact on extra-pulmonary organs such the heart and blood vessels as well as the metabolic system. In addition, the effects of COPD increases the risks of other conditions with breathlessness, inactivity, and exacerbations resulting in depression, anxiety, and inactivity with resulting osteoporosis risk and muscle loss. Finally, COPD treatment may in itself increase the risk of other conditions particularly those related to oral steroid usage.

So what are the implications for management? Clearly, patients need a comprehensive assessment identifying and addressing co-morbidities. This should ideally be provided in a comprehensive way rather than a patient with COPD having fragmented care from a broad range of health professionals. This would include addressing common risk factors ie, age, smoking, and poor self-management of the primary chronic disease. Treatments need to be assessed that may address the systemic effects of COPD such the PDE-4 inhibitors and statins (Fabbri and Rabe 2007). Improving specific COPD outcome will improve some of its secondary effects such as depression and immobility. Finally, attempts should be made to minimise iatrogenic effects of COPD treatment particularly oral steroid therapy is clearly important.