The asthma-COPD overlap syndrome (ACOS): hype or reality?

Abstract

SummaryAsthma-COPD Overlap Syndrome (ACOS) has been recently defined as a new pathological entity. Most studies support a large difference in the pathophysiology of bronchial asthma and chronic obstructive pulmonary disease (COPD). However, there is evidence of an increasing prevalence of patients in whom the two diseases coexist or in which one condition evolves into the other, leading to the pathological condition named ACOS. This occurs mainly in individuals with long-standing asthma, especially if also current or formersmokers. Indeed, epidemiological studies show that aging is one of the main risk factors for ACOS, creating the basis for the two entities to converge on the same subject. It is important not to forget the history of asthma, even when the patient develops functional and radiological features suggestive of COPD, because of the therapeutic implications. Patients with ACOS have poorer health related quality of life and higher exacerbation rate then subjects with asthma or COPD alone. Whether ACOS is a distinct nosological entity with genetic variants, or whether it is rather a condition of concomitant diseases that overlap is still a matter of debate. The challenge is to solve this issue. KEY WORDS: asthma; COPD; lung function; airway inflammation; quality of life; acute exacerbations.© C I C E d i z i o n i I n t e r n a z i o n a l i obstruction, chronic obstructive bronchitis and COPD with a reversible component. The crucial question is whether ACOS can be envisaged as a distinct nosological entity, or whether it is rather a condition of concomitant diseases that overlap. This is not a trivial issue, since the diagnostic and therapeutic approaches may considerably vary. If one disease (i.e. asthma) is the driving pathological condition and the other (i.e. COPD) occurs at some stages because of causal factors (i.e. smoking exposure), then the diagnostic procedures should aim at recognizing the primary nosological condition (i.e. reversibility test), and the pharmacological management would therefore follow current guidelines (i.e. inhaled combination treatment). Similar reasoning (with different conclusions) applies when the primary disease is COPD. In this scenario, the "overlap" state is by no means different from other overlapping conditions, such as COPD and sleep apnea syndrome, COPD and bronchiectasis, or asthma and rhinosinusitis, asthma and gastroesophageal reflux. The concept can be extended to extra-respiratory diseases (i.e. cardiovascular diseases) or even physiological abnormalities (i.e. obesity). On the other hand, the identification of a single genetic origin, together with common physiological abnormalities, lead to the description of a new nosological entity, which is not asthma nor COPD, but resembles features of both. The reason why this entity is being increasingly recognized only in recent years could be attributed to the increased life expectancy, since this condition is predominant in the most advanced ages. The challenge is to answer the question of whether ACOS is a hy...