Asthma-COPD overlap (ACO) is when a patient has symptoms of both asthma and chronic obstructive pulmonary disease (COPD). These patients experience frequent exacerbations, have worse quality of life, a more rapid decline in lung function and higher mortality, and consume a disproportionate amount of healthcare resources than either asthma or COPD alone.1
Chronic obstructive pulmonary disease (COPD) is defined as “a common, preventable and treatable disease that is characterised by persistent respiratory symptoms and airflow limitation that is due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles or gases.”2
The World Health Organization (WHO) estimates that COPD will rank as the world’s third leading cause of death by 2030.3
An estimated 1.2 million people are living with diagnosed COPD in the UK, considerably more than the 835,000 estimated by the Department of Health in 2011. In terms of diagnosed cases, this makes COPD the second most common lung disease in the UK, after asthma. Around 2% of the whole population—4.5% of all people aged over 40—live with diagnosed COPD.
Research from the British Lung Foundation also suggests that prevalence is growing. The number of people who have ever had a diagnosis of COPD has increased by 27% in the last decade, from under 1,600 to nearly 2,000 per 100,000.4
There are also 5.4 million people in the UK who are currently receiving treatment for asthma, of this 4.3 million are adults (1 in 12).5
Asthma prevalence is thought to have plateaued since the late 1990s, although the UK still has some of the highest rates in Europe and on average three people a day die from asthma. In 2016, 1,410 people died from asthma. The NHS spends around one billion a year treating and caring for people with asthma.
Asthma-COPD overlap syndrome (ACOS) or asthma-COPD overlap captures the subset of patients with airways disease who have features of both asthma and COPD.
It is characterised by persistent airflow limitation with several features usually associated with asthma, and several features usually associated with COPD. Making an accurate diagnosis depends on taking a good and detailed medical history to confirm exposure to risk factors, to characterise the symptoms (including provoking and relieving factors and variability) and to confirm that the patient has airflow obstruction using spirometry.1
Patients with ACOS often experience frequent exacerbations,6 have a worse quality of life, a more rapid decline in lung function, and higher mortality.7,8 In patients with overlap syndrome, both medical utilisation and cost were higher than in COPD patients without asthma.9
Subjects with ACOS represent a large proportion of COPD patients (~27%), and they form a distinct clinical phenotype with unique characteristics in comparison to patients with only COPD.
These subjects are more likely to be younger, have less smoking history, with a high BMI, but exhibiting a similar degree of severity in terms of spirometry and the six-minute walking distance. In addition, subjects with ACOS were more likely to have frequent and severe respiratory exacerbations than in those with either disease alone. However, the clinical distinction between the two obstructive diseases is not always clear.10
The Global Initiative for Asthma (GINA) and the Global Initiative for Chronic Obstructive Lung Disease (GOLD) initially proposed guidelines for “asthma and COPD overlap syndrome (ACOS)”,2 in which they recommended that the condition be defined in two steps.
Using these guidelines, the first step is the identification of a history of chronic airway disease, ie, chronic or recurrent cough, sputum production, wheezing, or repeated acute lower respiratory tract infections. In the second step, the features of asthma and those of COPD that best describe the patient (ie, age at onset, pattern of symptoms, results of pulmonary function tests, and findings on chest radiographs) are identified and compared, and the diagnosis is selected from the differentials of asthma, COPD, and ACOS.1,11
Spirometry is then recommended for confirmation of the diagnosis. Recommendation for specialised referral is the final step.1
The treatment recommendation for patients, whose differential diagnosis is equally balanced between asthma and COPD, is to start treatment for asthma until further investigations are performed.
The GINA/GOLD guideline recommends using an inhaled corticosteroid in a low or moderate dose (depending on level of symptoms); add-on treatment with long-acting beta2 agonists (LABA) and/or long-acting muscarinic antagonists (LAMA) is usually also necessary.
If there are features of asthma, avoid LABA monotherapy. This approach recognises the pivotal role of inhaled corticosteroids in preventing morbidity and even death in patients with uncontrolled asthma symptoms, for whom even seemingly ‘mild’ symptoms (compared to those of moderate or severe COPD) might indicate significant risk of a life-threatening attack.1
A recent analysis found that ACOS patients have a more severe symptom profile and experienced more sputum, chest tightness, wheezing and night-time and daytime symptoms than those with COPD-only or asthma-only, although other comorbidities may have been responsible for these symptoms.12
The analysis also found that the majority of patients with ACOS in the study were currently receiving treatment more closely aligned with a COPD-only diagnosis. The authors suggested that the greater use of triple therapy in patients with ACOS versus those with asthma-only is to be expected, given the opposing disease severity profiles of ACOS and asthma and the lack of approved triple therapies for asthma at the time of the survey.12
A considerable proportion of patients with ACOS in the study did not receive any form of ICS therapy and were potentially suboptimally treated according to GINA/GOLD guidelines, increasing the risk of symptoms and exacerbations.
Estimates of the prevalence of ACOS have ranged from 12% to 55% of patients with chronic obstructive airway diseases.12 Epidemiological studies show that in older people with obstructive airway disease, as many as half or more may have overlapping diagnoses of asthma and COPD (overlap syndrome). Overlap syndrome is recognised by the coexistence of increased variability of airflow in a patient with incompletely reversible airway obstruction.7
Alison Bloomer, Managing editor, GM
Conflict of interest: none declared.
2. https://goldcopd.org/gold-reports/ (accessed 20/10/18)
3. http://www.who.int/respiratory/copd/World_Health_Statistics_2008/en/ (accessed 20/10/18)
4. https://statistics.blf.org.uk/copd (accessed 20/10/18)
5. https://www.asthma.org.uk/about/media/facts-and-statistics/ (accessed 20/10/18)