Rhinosinusitis in ACO: What Is the Implication of Nasal Comorbidity?

The airway is subdivided into the upper and lower airway, but similar anatomical and morphological features and the immunological relationship between the two have led to the concept of “united airway disease” (UAD). Allergic rhinitis and asthma are the classic UAD, although there is considerable evidence that UAD may involve other clinical phenotypes of sinonasal disease (e.g., chronic rhinosinusitis [CRS]) and lower-airway disease (e.g., chronic obstructive pulmonary disease [COPD] and asthma-COPD overlap [ACO]). The data relating to the association between ACO and CRS is limited, and the present paper aims to review the concept of UAD in the context of ACO and CRS, providing a comprehensive description of the state of the literature and highlighting avenues for future research.