Impact of sinus surgery on type 2 airway and systemic inflammation in asthma

Tissue Eosinophils Threshold and its Association with Adult-Onset Asthma in Chronic Rhinosinusitis

INTRODUCTION

Tissue eosinophil counts (TEC) might serve as a biomarker linking chronic rhinosinusitis (CRS) and the presence of adult-onset asthma. This study aimed to determine if TEC in sinus mucosa/polyps in CRS patients is an independent indicator of asthma and to identify its optimal cut-off point.

METHODS

This cross-sectional study was conducted on primary CRS patients scheduled for surgery. All patients were assessed by a pulmonologist for asthma diagnosis. Tissues were collected during surgery and evaluated for TEC. Logistic regression and receiver operating characteristic analysis were used to determine significant factors and the optimal cut-off points of TEC associated with asthma.

RESULTS

A total of 103 CRS patients were included. Ten patients (9.7%) had underlying asthma, while 13 (12.6%) were first diagnosed by the pulmonologist. TEC ≥40 cells per high-powered field (HPF) exhibited a significant correlation with asthma (area under the curve = 0.71, p < 0.001). The sensitivity of this cut-off point was 0.70 (95% confidence interval [CI] = 0.47-0.87), and specificity was 0.66 (95% CI = 0.55-0.76). Positive predictive value and negative predictive value were 0.37 and 0.88, respectively. The cut-off point significantly associated with the presence of asthma, with an adjusted odds ratio of 3.13 (95% CI = 1.05-9.35, p = 0.04), controlling for polyps, allergic rhinitis, and computerized tomography (CT) score.

CONCLUSION

TEC in CRS patients can help determine the presence of adult-onset asthma, with an optimal threshold of ≥40 cells/HPF. This threshold is significantly associated with asthma independent of polyps, allergy, and CT score.

Relief of Airflow Limitation and Airway Inflammation by Endoscopic Sinus Surgery in a Patient with Severe Asthma with Eosinophilic Chronic Rhinosinusitis

Although endoscopic sinus surgery (ESS) is beneficial in improving asthma symptoms, its impact on the lung function in patients with asthma and chronic rhinosinusitis remains unclear. We herein report a case of severe asthma with eosinophilic chronic rhinosinusitis, in which ESS substantially improved airflow limitation and concomitantly reduced fractional exhaled nitric oxide and blood eosinophil counts. ESS likely relieved airflow limitation by suppressing type 2 inflammatory pathways. This case highlights ESS as a promising strategy for achieving clinical remission in patients with severe asthma and chronic rhinosinusitis.

Precision medicine to personalize medicine in allergic airway disease

PURPOSE OF REVIEW

The purpose of this study is to understand the approach to precision medicine and personalized medicine in the management of allergic airway disease.

RECENT FINDINGS

Identification of biomarkers as key tools used in precision medicine has led to the development of multiple biologic drugs being used as new treatments for allergic airway disease.

SUMMARY

In addition to these advances, there is still much needed effort to improve the feasibility and utility of integrating biologic omics data of precision medicine with physicochemical, behavioral, psychological, and social data to deliver optimized treatments that is personalized for each individual.

EUFOREA/EPOS2020 statement on the clinical considerations for chronic rhinosinusitis with nasal polyps care

Following the European Forum for Research and Education in Allergy and Airway Diseases (EUFOREA) treatment algorithm for chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP), patients suffering from severe uncontrolled CRSwNP are recommended to receive oral corticosteroids, (revision) sinus surgery, systemic biologicals and/or aspirin treatment after desensitization (ATAD). Given the major differences in indications, outcomes, practical considerations, risks and costs of these key pillars of treatment, there is a growing need to define criteria for each treatment option and list the clinically relevant and major considerations for them. This EUFOREA document therefore provides an expert panel overview of the expected outcomes, specific considerations and (contra)indications of the five major treatment arms of severe uncontrolled CRSwNP: oral corticosteroids, primary and revision sinus surgery, biological treatment and ATAD. This overview of treatment considerations is needed to allow physicians and patients to consider the different options in the context of providing optimal and personalized care for severe uncontrolled CRSwNP. In conclusion, the five major treatment options for severe uncontrolled CRSwNP have intrinsic advantages, specific indications and considerations that are of importance to the patient, the physician and the society. This EUFOREA statement supports the unmet need to define criteria for the indication of every treatment pillar of CRSwNP.

Allergy and Asthma Prevalence and Management Across Nasal Polyp Subtypes

Allergy and asthma prevalence vary across different subsets of chronic rhinosinusitis with nasal polyposis. In this article, the authors investigate the management of allergy and asthma within populations of patients with aspirin-exacerbated respiratory disease, allergic fungal rhinosinusitis, and central compartment atopic disease. Topical steroids, nasal rinses, and endoscopic sinus surgery are frequently employed in the management of nasal polyposis. Further, other causes of upper and lower airway inflammation like allergy and asthma should be considered in the overall treatment plan in order to optimize outcomes.

Effects of Endoscopic Sinus Surgery for Eosinophilic Chronic Rhinosinusitis on Respiratory Functions and FeNO Production in the Lower Respiratory Tract

OBJECTIVE

To confirm the relevance of upper and lower airway inflammation in eosinophilic chronic rhinosinusitis (ECRS), the effects of endoscopic sinus surgery (ESS) on lower airway functions and inflammation need to be examined in ECRS patients.

METHODS

Chronic rhinosinusitis patients with nasal polyps (25 non-ECRS, 28 ECRS) were enrolled. The 12 patients in the ECRS group had comorbid asthma, in contrast to none in the non-ECRS group. We divided ECRS patients into 2 groups of ECRS with and without asthma. Clinical markers, including fraction of exhaled nitric oxide (FeNO), respiratory functions, and the Asthma Control Test (ACT) questionnaire, were investigated before and after ESS.

RESULTS

The FeNO levels in the ECRS with asthma group decreased after ESS. The mean FeNO levels in this group were 56.3 ppb before ESS and 24.9, 25.1, 25.0, and 15.5 ppb 1, 2, 3, and 4 months, respectively, after ESS. The mean forced expiratory rates in 1 second before and after ESS were 67.6% and 73.0%, respectively. The mean maximal expiratory flow rates at 50% of the vital capacity before and after ESS were 45.8% and 58.0%, respectively. Significant differences were observed in respiratory functions before and after ESS. The mean ACT scores in the ECRS with asthma group before and after ESS were 17.5 and 23.5, respectively. The ACT scores were significantly higher after than before ESS.

CONCLUSIONS

The present results indicate that ECRS and bronchial asthma are common eosinophilic airway inflammatory diseases, and ESS for eosinophilic sinusitis may improve lower airway function.

Management paradigms for chronic rhinosinusitis in individuals with asthma: An evidence-based review with recommendations

BACKGROUND

Despite the significant morbidity associated with chronic rhinosinusitis (CRS) in individuals with asthma (CRSwA), there is a paucity of codified, evidence-based management strategies for CRS in this population.

METHODS

Using PubMed, Embase, and Cochrane Review Databases, a systematic review was performed covering management strategies for CRSwA. A total of 5903 articles were screened, and 70 were included for full-text analysis. After application of exclusion criteria, 53 articles comprised the qualitative synthesis. The level of evidence was graded and benefit-harm assessments, as well as value judgment and recommendations, were provided RESULTS: Strong evidence confirms the benefit of oral and topical medications on sinonasal-specific outcomes in individuals with CRSwA; there is low-grade evidence demonstrating that these agents improve lung function and/or asthma control. Moderate to strong evidence suggests that endoscopic sinus surgery (ESS) improves both sinonasal- and asthma-specific quality of life. Although there is insufficient to low evidence to indicate that ESS improves pulmonary function in this population, data indicate a positive impact of this intervention on asthma control. Biologic medications strongly improve both subjective and objective sinonasal- and asthma-specific outcomes.

CONCLUSION

Evidence supports managing CRS in individuals with CRSwA in a stepwise fashion, starting with traditional nonbiologic oral and topical medication, and escalating to second-line treatments, such as ESS and biologics. Optimal treatment of individuals who have CRSwA often requires concurrent, directed management of asthma, as not all CRS interventions impact asthma status.

Direct economic burden 1 year postoperation in Chinese adult patients with chronic rhinosinusitis with nasal polyps

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) remains a common and challenging clinical entity, and its economic burden has not been well described in China thus far.

METHODS

A total of 101 CRSwNP patients who underwent endoscopic sinus surgery were included to investigate direct costs in the first year post-surgery. Costs for outpatient visits, medication use, and examination costs were obtained from the Hospital Information System, and differences were compared between subgroups. Multiple linear regression analysis was adopted to investigate the main influencing factors on annual total direct costs for CRSwNP patients.

RESULTS

Ninety-two subjects completed the study. The individual mean total direct cost for a CRSwNP patient 1 year post-surgery was $742.4. The largest contributors were pharmacy costs ($580.2), followed by examination costs ($108.1) and outpatient visits ($54.1). Total direct costs were higher in subgroups of patients with uncontrolled clinical status, asthma comorbidity, and eosinophilic CRSwNP compared to their counterparts. The main influencing factors were clinical control status (P = 0.016) and asthma comorbidity (P = 0.035).

CONCLUSIONS

The individual mean total direct cost of CRSwNP in 1-year post-surgery was $742.4. Clinical control status and asthma comorbidity influence these costs and are therefore important in guiding health resources allocation for CRSwNP management.

Blood Basophils Relevance in Chronic Rhinosinusitis with Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) is characterized by eosinophilic asthma, chronic rhinosinusitis with nasal polyps (CRSwNP) and intolerance to cyclooxygenase-1 inhibitors. Interest is emerging in studying the role of circulating inflammatory cells in CRSwNP pathogenesis and its course, as well as their potential use for a patient-tailored approach. By releasing IL-4, basophils play a crucial role in activating the Th2-mediated response. The main aim of this study was to, first, investigate the level of the pre-operative blood basophils' values, blood basophil/lymphocyte ratio (bBLR) and blood eosinophil-to-basophil ratio (bEBR) as predictors of recurrent polyps after endoscopic sinus surgery (ESS) in AERD patients. The secondary aim was to compare the blood basophil-related variables of the AERD series (study group) with those of a control group of 95 consecutive cases of histologically non-eosinophilic CRSwNP. The AERD group showed a higher recurrence rate than the control group (p < 0.0001). The pre-operative blood basophil count and pre-operative bEBR were higher in AERD patients than in the control group (p = 0.0364 and p = 0.0006, respectively). The results of this study support the hypothesis that polyps removal may contribute to reducing the inflammation and activation of basophils.

Consensus on the management of united airways disease with type 2 inflammation: a multidisciplinary Delphi study

BACKGROUND

Scientific evidence on patients with multimorbid type 2 asthma and chronic rhinosinusitis with nasal polyps (CRSwNP) from a united airways disease (UAD) perspective remains scarce, despite the frequent coexistence of these entities. We aimed to generate expert consensus-based recommendations for the management of UAD patients.

METHODS

Using a two-round Delphi method, Spanish expert allergists, pulmonologists and otolaryngologists expressed their agreement on 32 statements (52 items) on a 9-point Likert scale, classified as appropriate (median 7-9), uncertain (4-6) or inappropriate (1-3). Consensus was considered when at least two-thirds of the panel scored within the range containing the median.

RESULTS

A panel of 30 experts reached consensus on the appropriateness of 43 out of the 52 (82.7%) items. The usefulness of certain biomarkers (tissue and peripheral blood eosinophil count, serum total IgE, and fraction of exhaled nitric oxide [FeNO]) in the identification and follow-up of type 2 inflammation, and assessment of the response to biologics, were agreed. Some of these biomarkers were also associated with disease severity and/or recurrence after endoscopic sinus surgery (ESS). Consensus was achieved on treatment strategies related to the prescription of anti-IL-4/IL-13 or anti-IgE agents, concomitant treatment with systemic corticosteroids, and combining or switching to biologics with a different mechanism of action, considering a number of UAD clinical scenarios.

CONCLUSION

We provide expert-based recommendations to assist in clinical decision-making for the management of patients with multimorbid type 2 asthma and CRSwNP. Specific clinical trials and real-world studies focusing on the single-entity UAD are required to address controversial items.

Cutoff Values of MASK-air Patient-Reported Outcome Measures

BACKGROUND

In clinical and epidemiological studies, cutoffs of patient-reported outcome measures can be used to classify patients into groups of statistical and clinical relevance. However, visual analog scale (VAS) cutoffs in MASK-air have not been tested.

OBJECTIVE

To calculate cutoffs for VAS global, nasal, ocular, and asthma symptoms.

METHODS

In a cross-sectional study design of all MASK-air participants, we compared (1) approaches based on the percentiles (tertiles or quartiles) of VAS distributions and (2) data-driven approaches based on clusters of data from 2 comparators (VAS work and VAS sleep). We then performed sensitivity analyses for individual countries and for VAS levels corresponding to full allergy control. Finally, we tested the different approaches using MASK-air real-world cross-sectional and longitudinal data to assess the most relevant cutoffs.

RESULTS

We assessed 395,223 days from 23,201 MASK-air users with self-reported allergic rhinitis. The percentile-oriented approach resulted in lower cutoff values than the data-driven approach. We obtained consistent results in the data-driven approach. Following the latter, the proposed cutoff differentiating "controlled" and "partly-controlled" patients was similar to the cutoff value that had been arbitrarily used (20/100). However, a lower cutoff was obtained to differentiate between "partly-controlled" and "uncontrolled" patients (35 vs the arbitrarily-used value of 50/100).

CONCLUSIONS

Using a data-driven approach, we were able to define cutoff values for MASK-air VASs on allergy and asthma symptoms. This may allow for a better classification of patients with rhinitis and asthma according to different levels of control, supporting improved disease management.

Current Understanding of the Role of Eosinophils in CRSwNP and Implications for Treatment with Mepolizumab and Benralizumab

BACKGROUND

International consensus statements now subdivide chronic rhinosinusitis (CRS) into several phenotypes and endotypes, including the presence of polyps (CRSwNP) and eosinophilia (eCRSwNP). Biological treatments aimed at blocking eosinophilic inflammation in CRSwNP via interleukin 5 (IL5) or the interleukin 5 receptor (IL5R) have demonstrated limited efficacy thus far.

OBJECTIVE

To review the pathophysiology of eCRSwNP, the evidence for mepolizumab (anti-IL5) and benralizumab (anti-IL5R) in CRSwNP, and to highlight areas for future research and therapeutic intervention.

METHODS

Primary and secondary literature search.

RESULTS

Clinical trials on mepolizumab and benralizumab in CRSwNP are limited and restricted by trial design which prevents direct comparison with other interventions, including surgery. Both agents would appear to provide some benefit in reducing nasal polyp size but limited clinical patient benefit. Molecular biological research highlights that eCRSwNP can occur in the absence of IL5 and that other cells/cytokines play an important part in the disease's pathophysiology.

CONCLUSION

Blockade of IL5/IL5R alone would appear to provide limited "real life" clinical benefit in patients with CRSwNP due to the complexities of the pathophysiology of the condition. Therapy aimed at several simultaneous cytokine targets has logic but well-designed trials are unlikely to be forthcoming in the short term due to the financial cost and commercial conflicts of interest.

A Decade of Clinical Advances in Chronic Rhinosinusitis: 2012-2022

The field of chronic rhinosinusitis (CRS) is constantly evolving. In the past 10 years, key advancements in basic and translational research as well as clinical studies have improved our understanding and management of CRS. Notably, treatment options have expanded to include novel therapeutic drugs, devices, and surgical techniques. Assessments of patient symptoms and their impact on quality of life have become more standardized. Progress has also been made in both determining the true prevalence of CRS and recognizing comorbidities that can impact CRS severity. Practice guidelines have also shifted from expert opinion to more data-driven analyses. This review highlights major clinical advancements made in the field of CRS over the past 10 years as well as identifies current gaps in knowledge that can form the basis for new areas of study over the next decade.

Management of Patients with Severe Asthma and Chronic Rhinosinusitis with Nasal Polyps: A Multidisciplinary Shared Approach

Chronic rhinosinusitis (CRS) is one of the most frequent comorbidities associated with asthma and it contributes to an amplified global disease burden in asthmatics. CRS prevalence is much higher in asthmatic patients compared to the general population and it is more frequently related to severe asthma, especially in presence of nasal polyps (chronic rhinosinusitis with nasal polyps, CRSwNP). Moreover, asthma exacerbation has a higher occurrence in CRSwNP. From a pathologic point of view, CRS and asthma share similar and connected mechanisms (e.g., type-2 inflammation). A multidisciplinary approach represents a crucial aspect for the optimal management of patients with concomitant asthma and CRSwNP and improvement of patient quality of life. An Italian panel of clinicians with different clinical expertise (pulmonologists, ear, nose and throat specialists, immunologists and allergy physicians) identified three different profiles of patients with coexisting asthma and nasal symptoms and discussed the specific tracks to guide a comprehensive approach to their diagnostic and therapeutic management. Currently available biological agents for the treatment of severe asthma act either on eosinophil-centered signaling network or type-2 inflammation, resulting to be effective also in CRSwNP and representing a valid option for patients with concomitant conditions.

Real-life effectiveness of dupilumab in patients with mild to moderate bronchial asthma comorbid with CRSwNP

BACKGROUND

Dupilumab, an anti-IL-4α receptor antibody, is a new treatment for severe or refractory asthma. However, real-world evidence on the efficacy of dupilumab in patients with mild to moderate bronchial asthma is lacking.

METHODS

We retrospectively evaluated the effects of dupilumab in 62 patients who received dupilumab for eosinophilic sinusitis comorbid with asthma at a single centre in Japan. Type 2 inflammatory markers, ACT, respiratory function tests, and forced oscillation technique (FOT) were analysed before, three months after, and one year after dupilumab administration, mainly in patients with mild to moderate asthma.

RESULTS

FEV1, %FEV1, %FVC, treatment steps for asthma and ACT improved significantly after three months of dupilumab treatment. FeNO was markedly decreased, whereas IgE and eosinophil counts showed no significant changes. Pre- and post-treatment respiratory resistance (Rrs) and respiratory reactance (Xrs) correlated significantly with FEV1. Improvement in %FEV1 was associated with higher FeNO and higher serum IgE before dupilumab treatment.

CONCLUSION

Dupilumab treatment for sinusitis may improve respiratory functions, asthma symptoms, and asthma treatment reduction, even if the associated bronchial asthma is not severe.

Improvement in Health-Related Quality of Life with Dupilumab in Patients with Moderate-to-Severe Asthma with Comorbid Chronic Rhinosinusitis with/without Nasal Polyps: An Analysis of the QUEST Study

Patients with asthma frequently have comorbid chronic rhinosinusitis (CRS) with or without nasal polyps, increasing disease burden and complicating treatment. These post hoc analyses investigated disease-specific health-related quality of life (HRQoL) and general health status in the randomized, placebo-controlled QUEST study (NCT02414854) in patients treated with dupilumab for moderate-to-severe asthma with comorbid CRS. Patients received 300 mg of dupilumab or placebo every 2 weeks for 52 weeks. CRS HRQoL was assessed by the 22-item Sino-Nasal Outcome Test (SNOT-22; items scored 0-5). The 22 items are categorized into 5 domains (nasal, ear/facial, sleep, function, and emotion), and patients report the top 5 most important items affecting their health. General health status was assessed by Euro-QoL visual analog scale (EQ-VAS). Of 1902 patients, 382 (20.1%) self-reported comorbid CRS; 193 patients receiving dupilumab 300 mg q2w or matched placebo were included in this analysis. At baseline, the most impacted SNOT-22 domain was nasal, and general health status was below population norms. Patients rated "decreased sense of taste/smell," "nasal blockage," "cough," "reduced productivity," and "wake up tired" as the 5 most important SNOT-22 items affecting their health. Percentage change from baseline in SNOT-22 total score was significantly greater for dupilumab vs placebo at Weeks 24, 36, and 52 (all p < 0.05). Improvements from baseline were significantly greater for dupilumab vs placebo at Week 52 for all SNOT-22 domains (p < 0.05), except emotion. At Week 52, significant changes from baseline with dupilumab vs placebo were observed for all 5 most important SNOT-22 items affecting their health (all p < 0.05). EQ-VAS was significantly improved with dupilumab vs placebo by Week 12, with improvements sustained to Week 52 (all p < 0.01). In patients with moderate-to-severe asthma who self-reported comorbid CRS, dupilumab treatment vs placebo improved CRS-specific HRQoL and general health status.

Understanding the Cellular Sources of the Fractional Exhaled Nitric Oxide (FeNO) and Its Role as a Biomarker of Type 2 Inflammation in Asthma

Fractional exhaled nitric oxide (FeNO) has gained great clinical importance as a biomarker of type 2 inflammation in chronic airway diseases such as asthma. FeNO originates primarily in the bronchial epithelium and is produced in large quantities by the enzyme inducible nitric oxide synthase (iNOS). It should be noted that nitric oxide (NO) produced at femtomolar to picomolar levels is fundamental for respiratory physiology. This basal production is induced in the bronchial epithelium by interferon gamma (IFNγ) via Janus kinases (JAK)/STAT-1 signaling. However, when there is an increase in the expression of type 2 inflammatory cytokines such as IL-4 and IL-13, the STAT-6 pathway is activated, leading to overexpression of iNOS and consequently to an overproduction of airway NO. Increased NO levels contributes to bronchial hyperreactivity and mucus hypersecretion, increases vascular permeability, reduces ciliary heartbeat, and promotes free radical production, airway inflammation, and tissue damage. In asthmatic patients, FeNO levels usually rise above 25 parts per billion (ppb) and its follow-up helps to define asthma phenotype and to monitor the effectiveness of corticosteroid treatment and adherence to treatment. FeNO is also very useful to identify those severe asthma patients that might benefit of personalized therapies with monoclonal antibodies. In this review, we revised the cellular and molecular mechanisms of NO production in the airway and its relevance as a biomarker of type 2 inflammation in asthma.

Sequential Biotherapy Targeting IL-5 and IL-4/13 in Patients with Eosinophilic Asthma with Sinusitis and Otitis Media

Type 2 (T2) inflammation plays an important role in the pathogenesis of allergic diseases such as asthma, eosinophilic chronic rhinosinusitis (ECRS), or eosinophilic otitis media (EOM). Currently, in severe asthma with the T2 phenotype, biologics targeting mediators of T2 inflammation dramatically improve the management of severe asthma. While treatment with a single biologic is common, little is known about cases of the sequential use of two biologics. Here, we report a case of severe asthma with refractory ECRS and EOM in which total control of these allergic diseases could not be achieved with a single biologic but could be achieved via the sequential use of the anti-IL-5 receptor antibody and human anti-IL-4/13 receptor monoclonal antibody. It is suggested that it is necessary to control multiple T2 inflammatory pathways to achieve total control of severe allergic diseases. Sequential biotherapy may help solve the clinical challenges associated with single-agent molecular-targeted therapies.

Feasibility of Discontinuing Biologics in Severe Asthma: An Algorithmic Approach

In severe asthma with type 2 (T2) inflammation, biologics targeting key mediators of T2 inflammation, including interleukin (IL)-5, IL-4/IL-13, and immunoglobulin (Ig)E, remarkably improve the management of severe asthma, providing new insights into the clinical course of asthma such as disease modification and broad modulation of T2 inflammation. Once severe asthma has become a “controllable” condition, the question of discontinuation of biologics arises due to cost and side effects. The studies on discontinuing biologics in asthma demonstrate that some of patients successfully discontinue biologics, indicating that it is a feasible option in a subset of patients. Incorporating the evidence of discontinuation, we propose the criteria for the discontinuation of biologics. Our proposed criteria for the discontinuation of biologics consist of an absence of asthma symptoms (asthma control questionnaire [ACQ] score < 1.5 or asthma control test [ACT] score > 19), no asthma exacerbations, no use of oral corticosteroids, normalized spirometry (forced exhaled volume in 1 second [FEV₁] ≥ 80%), suppressed T2 inflammation (blood eosinophil counts < 300 μL and fractional exhaled nitric oxide [FeNO] < 50 ppb), and control of asthma comorbidities. Real-world evidence verified a subset of patients achieving highly well-controlled conditions after use of biologics, namely super-responders, who are candidates for the discontinuation of biologics. If super-responders meet all of the criteria, they are allowed to discontinue biological therapies. Our proposed algorithm may support physicians’ treatment decisions for patients receiving biologics.

An official JRS statement: The principles of fractional exhaled nitric oxide (FeNO) measurement and interpretation of the results in clinical practice

Nitric oxide (NO) is produced in the body and has been shown to have diverse actions in the abundance of research that has been performed on it since the 1970s, leading to Furchgott, Murad, and Ignarro receiving the Nobel Prize in Physiology or Medicine in 1998. NO is produced by nitric oxide synthase (NOS). NOS is broadly distributed, being found in the nerves, blood vessels, airway epithelium, and inflammatory cells. In asthma, inflammatory cytokines induce NOS activity in the airway epithelium and inflammatory cells, producing large amounts of NO. Measurement of fractional exhaled nitric oxide (FeNO) is a simple, safe, and quantitative method of assessing airway inflammation. The FeNO measurement method has been standardized and, in recent years, this noninvasive test has been broadly used to support the diagnosis of asthma, monitor airway inflammation, and detect asthma overlap in chronic obstructive pulmonary disease (COPD) patients. Since the normal upper limit of FeNO for healthy Japanese adults is 37 ppb, values of 35 ppb or more are likely to be interpreted as a signature of inflammatory condition presenting features with asthma, and this value is used in clinical practice. Research is also underway for clinical application of these measurements in other respiratory diseases such as COPD and interstitial lung disease. Currently, there remains some confusion regarding the significance of these measurements and the interpretation of the results. This statement is designed to provide a simple explanation including the principles of FeNO measurements, the measurement methods, and the interpretation of the measurement results.