Year : 2015 | Volume
: 29 | Issue : 1 | Page : 1--2
Asthma and chronic obstructive pulmonary disease overlap syndrome: Decoding the enigma
SN Gaur, Gaurav Bhati
Department of Pulmonary Medicine, Vallabhbhai Patel Chest Institute, University of Delhi, New Delhi, India
S N Gaur
Department of Pulmonary Medicine, Vallabhbhai Patel Chest Institute, University of Delhi, New Delhi
|How to cite this article:|
Gaur S N, Bhati G. Asthma and chronic obstructive pulmonary disease overlap syndrome: Decoding the enigma.Indian J Allergy Asthma Immunol 2015;29:1-2
|How to cite this URL:|
Gaur S N, Bhati G. Asthma and chronic obstructive pulmonary disease overlap syndrome: Decoding the enigma. Indian J Allergy Asthma Immunol [serial online] 2015 [cited 2020 Jan 18 ];29:1-2
Available from: http://www.ijaai.in/text.asp?2015/29/1/1/162968
Asthma and chronic obstructive pulmonary disease (COPD) are the common obstructive airway diseases. Asthma is recognized as an allergic disease that develops mostly in childhood, in atopic individuals usually characterized by reversible airflow obstruction, has an episodic course, responding well to treatment and generally has a good prognosis.  In contrast, COPD is typically caused by tobacco smoking, or exposure to noxious particles or fumes.  It is a disease of mid to later part of life and is characterized by incompletely reversible airflow limitation that results in a progressive decline in lung function ultimately leading to premature death. There is a need to re-evaluate the concept of asthma and COPD as separate conditions, especially in situations when they may coexist, or when one condition may evolve into the other. There are circumstances where the feature of asthma and COPD can overlap, or co-exist, and the Asthma COPD overlap syndrome (ACOS) is coined for such conditions.
Asthma symptoms can vary with time and season and can be triggered by various inflicting factors such as exercise, laughter, exposure to dust, or allergens. Spirometry shows variable airflow limitation with more than 12% reversibility with inhaled bronchodilator. COPD is usually seen above the age of 40 years, mostly in smokers, with chronic or continuous symptoms particularly during exercise with a generally progressive course despite treatment. COPD is characterized by fixed airflow limitations with <12% reversibility with inhaled bronchodilators with a history of exposure to noxious particles and gases. ACOS is seen above 40 years of age but may also have vague symptoms in childhood or early adulthood. Exertional dyspnea which is persistent but variability may be prominent. Airflow limitation which is not fully reversible is often present. Family history of asthma may also be present. ACOS shows a better response to treatment compared to COPD cases in terms of partial or significant reduction in symptoms. Radiological presentation in asthma is usually a normal skiagram, whereas hyperinflation is a predominant feature of both COPD and ACOS. 
Epidemiological studies show as many as half or more elderly patients with obstructive airway disease, may have overlapping diagnoses of asthma and COPD named as "overlap syndrome" which is increasingly considered to be a treatment-responsive disease. Thus, there is a need to re-evaluate the concept of asthma and COPD as two separate conditions. The current descriptions of asthma and COPD have been simplified into patterns of abnormal airway physiology which in conjunction with symptoms can be used to facilitate clinical recognition. There is a need to broaden these descriptions to accommodate the common clinical reality of people who fit the criteria for more than one condition.
It is difficult to distinguish between asthma and COPD in smokers, it is seen that asthmatic smokers have features resembling COPD, since they are less responsive to LABA and corticosteroids , and more likely to have increased airway neutrophilia. Incompletely reversible airway obstruction can also occur in long-standing asthma. Studies found that 16% of patients with asthma had developed poor airflow reversibility after 21-33 years. , Since overlap syndrome has features of both asthma and COPD such as the presence of chronic bronchitis and bacterial colonization, which usually resembles COPD rather than asthma. However, history of atopy which is seen in the majority of patients with asthma is not frequently seen in patients with overlap syndrome.  Increased thickness of the airway wall is an important feature leading to airway obstruction in most respiratory illness and impaired adult lung function. In asthma, this is attributed to inflammation, sub-epithelial fibrosis, and increased thickness of the smooth muscle and mucous glands. Increased thickness of the airway epithelium and goblet cell hyperplasia are features of the remodeled airway in both asthma and COPD.  Similarly, in overlap syndrome there is increased airway wall remodeling with increased bronchial wall thickening  on high-resolution computed tomography. Since overlap syndrome shares common features with asthma and COPD, it poses a challenge in terms of management, such as the need for oral or inhaled corticosteroids, antimuscarinics, LABAs, pulmonary rehabilitation, etc.
The overlap of morphologic findings, clinical findings, and evidence of variable expiratory airflow obstruction and reversibility can lead to an accelerated decline in lung function and poor lung growth in children.  These pathways share common risk factors of tobacco smoke exposure, BHR, asthma, and respiratory infections. These risk factors may in turn co-occur and potentiate each other. In studying the pathogenesis of overlap syndrome, it will be fruitful to look for mediators that drive both airway inflammation and airway remodeling. Since patients with overlap syndrome are usually excluded from randomized treatment trials, there is a need to extend drug efficacy studies to evaluate it as a separate clinical entity having overlapping asthma and COPD. It is also pertinent to mention that this entity needs to be investigated in terms of mechanisms and treatment, especially in patients of older age group having asthma and/or COPD.
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Conflicts of interest
There are no conflicts of interest.
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