The Unified Airway Hypothesis: Revisiting the Relationship Between Upper and Lower Airway Diseases
The unified airway hypothesis suggests that the entire respiratory system represents a functional unit that includes the nose, paranasal sinuses, larynx, trachea, and distal lung. For nearly two decades, researchers have accumulated evidence supporting the belief that many chronic inflammatory upper and lower airway diseases arise from a single pathological process and manifest in the airway in different locations. Recently, articles on the therapeutic targeting of eosinophils and the cytokine Interleukin-5 (IL-5) in patients with asthma, chronic rhinosinusitis with nasal polyps (CRWwNP), and aspirin-exacerbated respiratory disease have helped to illuminate this relationship.
In a collaborative paper published in the Journal of Allergy and Immunology: In Practice, authors from institutions around the world examined clinical trial and real-world data that may help clinicians improve patient care. Amber Luong, MD, PhD, professor and vice chair for academic affairs in the Department of Otorhinolaryngology at McGovern Medical School at UTHealth Houston, was among the authors.
“Based on our review of the literature, eosinophils and IL-5 have important pathophysiological roles in both the upper and lower airways, although the impact of eosinophils and IL-5 may vary in asthma and CRSwNP, which will require further investigation,” Dr. Luong says. “Pharmaceutical targeting of eosinophils and IL-5 in patients with upper, lower, and comorbid upper and lower airway inflammation has led to clinical benefit, supporting the hypothesis that these are linked conditions that manifest in different locations.
“Patients with inflammatory respiratory diseases typically present to otolaryngologists, pulmonologists, primary care physicians, and allergists,” she observes. “Given the strong comorbidity between asthma and chronic rhinosinusitis with nasal polyps, we should think about the involvement of upper airway inflammation in asthma patients and about inflammation of the lower airway in patients with rhinosinusitis. Viewing the airway as a functional unit can help us improve our clinical decision making and provide better patient care.”
Reference
Bachert C, Luong AU, Gevaert P, Mullol J, Smith SG, Silver J, Sousa AR, Howarth PH, Benson VS, Mayer B, Chan RH, Busse WW. The Unified Airway Hypothesis: Evidence From Specific Intervention with Anti-IL-5 Biologic Therapy. J Allergy Clin Immunol Pract. 2023 Sep;11(9):2630-2641.