Chronic Obstructive Pulmonary Disease (COPD) and asthma are common chronic diseases, with a worldwide prevalence of around 9 to 10%  for COPD and 1 to 18% for asthma . Although they represent two distinct entities, the disease processes and physical symptoms of both diseases overlap and can provoke a considerable burden on the daily lives of affected patients. The impact of these chronic conditions however, is not only characterized by a substantial physical burden, but also by the frequent occurrence of co-morbid affective problems like depression or anxiety .
Depression and Anxiety in Asthma and COPD
The prevalence of depression and anxiety in patients with COPD varies widely between studies [4–6]. Recently Zhang et al. did a systematic review, meta-analysis and meta-regression on the prevalence of depressive symptoms in patients with COPD; only studies including a healthy control group were eligible. They found that patients with COPD have a higher prevalence of depressive symptoms than healthy controls (24,6%, 95% CI: 20.0 - 28.6% vs. 11,7%, 95% CI: 9-15.1%) . For anxiety such a meta-analysis has not been conducted yet, however there is a review by Yohannes et al. on depression and anxiety in chronic heart failure and COPD. In their review Yohannes et al. report rates between 6 and 74% for self-reported symptoms of anxiety . In asthma there is less variation in the prevalence rates for depression (around 10%) and anxiety (between 12 to 50) [8, 9].
Asthma and COPD patients with co-morbid depression and/or anxiety tend to report an overall worse health status [5, 10]. In addition, prospective research in patients with COPD showed that higher depression scores were associated with higher exacerbation frequencies (for symptom-based exacerbations: adjusted IRR, 1.51; 95% CI, 1.01-2.24; for event-based exacerbations: adjusted IRR, 1.56; 95% CI, 1.02-2.40) , a higher risk of hospitalization during follow-up (adjusted IRR, 1.72; 95% CI, 1.04-2.85)  and higher mortality rates (hazard ratio, 1.93; 95% CI, 1.04-3.58 and OR, 2.74; 95% CI, 1.42-5.29, respectively) [11, 12] while anxiety was associated with increased overall length of exacerbations (1.92 times longer CI, 1.04-3.54) . Moreover, anxiety and depression may even be more decisive predictors of functional capacity in patients with COPD than physiological markers such as lung function (OR 1.13; 95% CI, 1.02-1.26; versus no significant result for FEV1) .
In asthma, depression appeared to be associated with less adequate medication use and a lower level of physical exercise [8, 9, 14], and anxiety with more asthma symptoms, higher medication use and a more frequent use of healthcare services . The latter, in turn, might explain the negative association that has been reported between anxiety and inflammation of the airways. Anxiety, as suggested, might lead to more prescription and/or greater consumption of corticosteroids which might result in less inflammation of the airways [9, 15–17].
Hence, co-morbid depression and anxiety in patients with asthma or COPD not only affect quality of life but also treatment outcomes. In clinical practice however, there is a considerable under-detection of anxiety and depression; less than half of the depressed and/or anxious patients are recognized . In patients with respiratory illnesses, recognizing depression or anxiety is further complicated due to overlap in symptoms, which makes a differential diagnosis difficult  and results in inadequate treatment of co-morbid depression and anxiety.
Only a few studies have examined how these co-morbid disorders should preferentially be treated [6, 20–23]. Most studies were conducted within secondary care settings and investigated the short-term effectiveness of one type of behavioral therapy (e.g. education, cognitive behavioral therapy (CBT), problem solving therapy (PST), or relaxation therapy) without monitoring of long term results [6, 20, 21]. A large primary care study on late life depression in a general population, however, showed that a collaborative care approach in which mood status is monitored, with subsequent intensification of treatment when necessary was more effective in treating depression than merely offering one type of treatment .