The terms unified airway or united airway describes the concept that inflammation affects upper and lower airways by similar mechanisms and diseases exhibit similar anatomical, histological and immunological features.
Unified airway pathophysiology may manifest as rhinitis, rhinosinusitis and nasal polyposis in the upper airway and asthma or bronchial inflammation in the lower airways.
The airway is an area of multidisciplinary crossover and multiple specialists may be involved (GPs, ENT surgeons, respiratory physicians and allergists). Each has their own clinical priorities and approach.
The clinical importance of the unified airway concept is that these conditions should not be investigated and treated as isolated entities, rather the diagnosis of lower airway inflammation should prompt workup of the upper airway, and vice versa. Several clinical studies demonstrate a bi-directional naso-bronchial relationship, where nasal stimulation can induce bronchial inflammation and lower airway provocation results in sinonasal inflammation.
The epidemiology also supports an interconnected airway model, 20-25% of patients with chronic rhinosinusitis (CRS) have asthma and 10% of asthmatics have CRS. In patients who have CRS with nasal polyps, rates of asthma are even higher (40-60%), which is associated with more severe asthma and poorer lung function (lower FEV, steeper FEV vs. age) – the equivalent of smoking a pack of cigarettes per day.
The coexistence of allergic rhinitis (AR) and asthma is higher still, 15-38% of AR patients have asthma and 80-100% of asthmatics meet diagnostic criteria for AR.
A range of other diseases are associated with the underlying inflammatory pattern (predominately eosinophilic, IgE mediated) and would benefit from review by an otolaryngologist as their diagnosis may be more challenging. These include allergic fungal rhinosinusitis, central compartment atopic disease, non-allergic rhinitis with eosinophilia syndrome and aspirin-exacerbated respiratory disease.
Granulomatous conditions such as sarcoidosis and granulomatosis with polyangiitis also cause concomitant upper and lower airway pathology based on their underlying inflammatory mechanisms.
The cornerstone of management in unified airway conditions addresses the underlying inflammation through topical and systemic medication, exposure minimisation and optimisation of comorbidities. Surgery plays an important role in the upper airway.
Topical mediation
Topical corticosteroids play a central role in unified airway disease, targeting the underlying inflammatory cascade. Asthma treatment is underpinned by long-acting beta agonists and inhaled corticosteroids. Steroid nasal sprays and rinses/douches are used to deliver medication to the nasal cavity and sinuses respectively in all sinonasal diseases (usually in mometasone or fluticasone).
These second-generation intranasal corticosteroids are safe for long-term use without treatment breaks as their systemic bioavailability is less than 1%. Patients are often concerned about long-term topical steroid side effects, particularly when using inhaled steroids for asthma as well, so taking time to allay these fears may pay long-term dividends.
Evidence suggests that only 20% of patients use their topical medication correctly. Adequate education and reinforcement of delivery technique and regular usage are essential.
Systemic steroids and biologics
Oral corticosteroids are commonly employed for acute flares of disease and when there is symptomatic progression despite optimised topical medication. They act in part by downregulating eosinophils and associated interleukins (IL-4, IL-5 etc).
Ideal dosage and duration are unclear and may range from five days to three weeks, but there is a growing body of evidence that they should be used with more caution and cumulative lifetime exposure of as little as one gram increases the risk of adverse events, such as type 2 diabetes. When a patient is prescribed two or more courses of oral corticosteroids within 12 months, alternatives such as surgery or biologics should be strongly considered.
Biologics are a group of monoclonal antibody medications targeting part of the (type 2) inflammation seen in rhinitis, sinusitis with polyps and severe asthma. While four agents have been licensed for many years in Australia for use in severe asthma, only last year was one (Mepolizumab) TGA approved for use in chronic sinusitis with nasal polyps, significantly improving the treatment options for severe/refractory nasal polyps. Omalizumab has been shown to significantly improve nasal scores in allergic rhinitis when used to treat asthma, although no biologics are currently licensed for AR alone.
Surgery
Nasal and sinus surgery are sometimes overlooked in management of the unified airway, despite being a vital part of the management of allergic rhinitis and chronic rhinosinusitis. They both reduce validated nasal symptom scores and improve quality of life scores. They act to enlarge the nasal airway, resulting in less obstruction and better topical delivery of medication.
Allergic rhinitis often benefits from turbinate reduction and CRS from endoscopic sinus surgery (ESS), both of which have been shown to improve asthma control.
In CRS patients without asthma, a study found that early ESS may decrease inflammatory burden and mitigate risk of developing asthma by a factor of 10. In CRS patients with comorbid asthma, ESS has been proven to improve clinical asthma outcomes measures (decreased asthma exacerbations, hospitalisations, and medication usage) and asthma control.
Key messages
- The unified airway concept highlights that inflammation affects the upper and lower airways by similar mechanisms
- A multidisciplinary, patient-focused approach comprehensively managing both upper and lower airway pathology together generally leads to improved overall outcomes across the entire airway
- Sinus and nasal surgery play an important role in managing combined airway disease.
Author competing interests – nil