Connecting the Airways: Current Trends in United Airway Diseases

The concept of united airway disease (UAD) highlights the bidirectional relationship between inflammatory disorders of the upper airways-such as allergic rhinitis and chronic rhinosinusitis with or without nasal polyps (CRSwNP/CRSsNP)-and lower airway diseases, most notably asthma. This paradigm is supported by epidemiological, embryological, and immunological evidence demonstrating that airway inflammation represents a single, interconnected process rather than isolated compartmental pathology. Central to many UAD phenotypes is type 2 (T2) inflammation, driven by cytokines including IL-4, IL-5, and IL-13, and mediated by effector cells such as eosinophils and group 2 innate lymphoid cells (ILC2s). Epithelial barrier dysfunction often serves as the initiating trigger for this shared inflammatory cascade by production of TSLP, IL-25 and IL-33. Optimal diagnosis and management of UAD require an integrated, multidisciplinary framework. Clinical evaluation remains essential for patient characterization but must be complemented by pheno-endotypic assessment using imaging (CT), allergy testing, biomarker profiling (FeNO, blood eosinophils, IgE), and pulmonary function testing (spirometry, impulse oscillometry). Therapeutic strategies are layered, targeting both symptom control and inflammation across airway compartments. Standard approaches include intranasal and inhaled corticosteroids as well as saline irrigations, while severe T2-high disease increasingly benefits from biologic therapies (anti-IL-5/IL-5R, anti-IL-4R, anti-TSLP), which reduce dependence on systemic corticosteroids and surgical interventions such as endoscopic sinus surgery (ESS). Emerging precision-medicine models, particularly the "treatable traits" approach, further underscore the need to view the airway as a unified system. Collectively, these insights reinforce the clinical imperative of addressing upper and lower airway disease as a continuum, ensuring that inflammation in one district is neither overlooked nor treated in isolation.