Eosinophilic esophagitis (EoE) is an allergic disease of the esophagus that affects both children and adults and is defined by clinical and histologic characteristics. Diagnostic criteria include eosinophilic infiltration of the esophagus with ≥ 15 Eosinophils/ high-powered field (Eos/HPF) in the setting of esophageal dysfunction in adults [1] and swallowing disturbances in children [2]. EoE is in remission if there are no symptoms, and the eosinophil count decreases to <15 eos/HPF in a patient with previously diagnosed EoE. Multiple endoscopies with biopsies are needed to know if patients respond to treatment. Ideally, non-invasive methods could supplement or replace upper endoscopy to facilitate the management of this disease [3]. There is a growing necessity for non-invasive biomarkers that can accurately diagnose this condition and assess response to therapy Fractionated exhaled nitric oxide (FeNO) has proven to be a valuable measure of disease activity in studies of patients with atopic diseases [4],  asthma [5], non-atopic lung diseases [6,7], and extrapulmonary diseases [8]. For this reason, the objective of this study is 1, to investigate whether FeNO levels are helpful for diagnostic and for evaluating response to therapy in patients with EoE. 2, To study whether there are differences between EoE patients and controls regarding age, sex, FeNO levels, presence of asthma and rhinitis. 3, Calculate the sensitivity, specificity, positive predictive value, and negative predictive value of FeNO levels. 108.

This prospective, descriptive, and analytical study of an only center includes patients diagnosed with EoE in a tertiary hospital in central Spain. The diagnosis of EoE was made according to consensus guidelines [1,-9] (≥ 15 Eos/HPF) (Figure 1) in the setting of esophageal dysfunction in adults and swallowing disturbances in children.

Figure 1. Esophageal epithelium with numerous eosinophils. HE X20 (Image courtesy of Drª. Lucia Gonzalez Jimenez. Pathological Anatomy Service of the General Hospital of Ciudad Real. Spain).

Figure 1. Esophageal epithelium with numerous eosinophils. HE X20 (Image courtesy of Drª. Lucia Gonzalez Jimenez. Pathological Anatomy Service of the General Hospital of Ciudad Real. Spain).

 We have studied FeNO levels in 204 patients, which were women 101 (49.5%). The median age of the patients in the study was 38, and FeNO levels were 19 ppb. They had EoE 71 EoE (35%), asthma 135 (66%), and rhinitis 121 (59%). Results of comparing patients with EoE and controls (Table1) There are significant differences between patients with EoE and control subjects in age (levels lower in patients with EoE), sex (EoE more frequent in men), and FeNO levels (higher in patients con EoE than in control subjects. If we eliminate the subjects who are non-asthmatic, FeNO levels are significantly higher in the patients with EoE than in the control subjects. We have not found significant differences between patients and control subjects, considering (the presence or absence of asthma and rhinitis, neither between female subjects, nor between male subjects and Feno-l, nor between FeNO levels in patients before and after treatment. We have found significant differences when we have recoded Feno levels (< and ≥30 parts per billion) and applied Chi-square Test (X2). (Tables 1 and 2).

Table 1: Comparison of 1.1. Patients’ (EoE) versus controls subjects (CS). 1.2. Fractionated exhaled nitric oxide levels (Feno-l) between patients and CS, considering the absence (1.2)/presence (1.3) of asthma. Patients’ and CS - with rhinitis, without asthma (1.4), without rhinitis and asthma (1.5), without rhinitis, with/without asthma (1.6).

Table 2: Results of 1.1 The recoding of FeNO-level to 30 parts/billion(ppb) in patients and controls/subject (CS) and Chi-square tests(X²). 1.2,1.3 Descriptive statistics and p-values of different study variables comparing patients and CS. 1.4 Comparison of FeNO-l before and after treatment using the Wilcoxon range test. 1.5 Sensitivity and specificity of FeNO-l.

In recent years, in patients with EoE, studies have been carried out on multiple posible biomarkers. Still, none has been valid for the diagnosis and or / to study the evolution of the  disease after treatment. Therefore, there is still no minimally invasive biomarker that has been incorporated into guideline recommendations or routine clinical practice [11]. We decided to study the role of FeNO in EoE because this biomarker  informs us of eosinophilic inflammation in the respiratory tract [12] and possibly, in other organs with similar inflammation. Since recent studies found elevated FeNO levels in atopic patients but without asthma, in anaphylaxis with respiratory symptoms [13], in non-asthmatic patients with Hodgkin´s lymphoma, in atopic dermatitis, and many other diseases (pulmonary and extrapulmonary), including bronchiectasis, chronic tonsillitis, infections of the upper respiratory tract, and lupus [14]. British guidelines have approved the use of FeNO as evidence of eosinophilic inflammation, and the American Thoracic Society (ATS) has recommended using FeNO levels

for monitoring eosinophilic ai ay inflammation [15].These observations suggest a possible role for FeNO in extra-respiratory diseases with th2 inflammation as EoE. The increased levels of inducible nitric oxide synthetase in the esophageal mucosa of patients with EE. Experiences upregulation during LTh2-mediated responses, such as they can be allergic responses or eosinophilic inflammatory processes. The result is an increased production of nitric oxide that can be transmitted through the esophagus and mixed with exhaled respiratory gases [16]. This would explain the measurement of the FeNO levels to reflect eosinophilic inflammation that occurs in the esophagus The role of FeNO levels has been studied in inflammatory bowel disease and correlates with disease activity3. Other gastrointestinal tract diseases, such as inflammatory esophageal diseases in which sphincter function may be altered, are also associated with elevated FeNO levels. When the esophageal sphincters function correctly, they maintain NO within the gastrointestinal tract [17]. Some gastrointestinal tracts can coexist with asthma. We also know that there is a high prevalence of gastroesophageal reflux disease (GERD) in asthmatics, and it can cause asthma [18]. Patients without atopic comorbidities found no correlation between FeNO levels and the presence or absence of inflammatory esophageal pathology.  The authors evaluated whether GERD impacted the FeNO levels in patients who did not suffer from respiratory tract disease. FeNO in patients with endoscopic gastroesophageal changes did not differ significantly from patients without inflammatory changes in the stomach and esophagus. Furthermore, the presence of a hiatal hernia did not affect FeNO levels. Therefore, the authors concluded that gastroesophageal pathologies did not significantly affect FeNO levels [18]. This could be explained because these diseases do not present with eosinophilic inflammation, nor are they atopic diseases. Another study also evaluated the influence of GERD on FeNO levels in patients with respiratory disease. A correlation was found between FeNO levels and a pH-meter performed in the group of patients with GERD. But this study concluded that GERD has Little influence on FeNO levels in asthmatic subjects [19]. Among the subjects of this study, we have found significant differences in age and sex since men predominate in the group of patients and are younger than the control subjects. These data are consistent with multiple epidemiological studies conducted over 15-20 years [14-20]. Epidemiologic associations between EoE and the other allergic manifestations have been well established, with atopic dermatitis, IgE-mediated food allergy, asthma, allergic rhinitis, and pollen food allergy syndrome. All are common comorbidities in EoE patients. Therefore, patients with atopic diseases are at increased risk of being diagnosed with EoE [20-22]. We have studied FeNO-l in EoE patients and Cs about two comorbidities (asthma and rhinitis). There are significant differences in patients with EoE with rhinitis (without asthma), in patients (with and without asthma), and patients with EoE (without asthma and rhinitis) since the patients with EoE have higher FeNO-l than control subjects [23,24]. Age, FeNO levels, and asthma or rhinitis in female or male patients with EoE do not differ from control subjects. We have not found studies with similar variables in patients with EoE to be able to compare results. There are few studies where that compare FeNO levels in patients with EoE before treatment (active EoE) and after treatment (EoE in remission) [3]. These results affirm that FeNO levels do not help evaluate the remission of EoE or the effectiveness of a specific treatment. Neither they nor we have found differences between both groups. Other studies on EoE conclude that FeNO levels likely have limited clinical utility for predicting the severity of esophageal eosinophilia [17]. Fortunately, several promising biomarkers are under study, which may reduce the need for repeated endoscopic biopsies [11]. In a study on patients with and without EoE, they calculate the high FeNO specificity (87%). Our results regarding the specificity of FeNO levels were somewhat lower (71.42%), while the sensitivity was similar in both studies (around 50%) [25]. we have recorded the FeNO-l to < and ≥ 30ppb (median 28). We have found significant differences for FeNO levels ≥30 parts per billion in non-asthmatic subjects with you. Therefore, the patient’s non-asthmatics with FeNO levels ≥30 parts per billion have the probability of having EoE, especially if they have symptoms of esophageal dysfunction. The problem is that there are few subjects with FeNO ≥ levels 30 parts per billion without asthma. The same is the opinion of the authors of a previously commented study since they conclude that the specificity of testing was high in patients with FeNO levels> 40 parts per billion. Still, very few patients reached these FeNO levels [16]. In asthma, specificity is optimized if a higher FeNO cut-off is used [26]. Something like what happens in asthma could occur in EoE in terms of specificity Our study has limitations, such as the number of determinations of FeNO-levels is small, especially in patients with non-asthmatic esophagitis. But on the other hand, it has the strength that it is a prospective study that, in addition to studying the usefulness of FeNO-levels in the diagnosis and the evolution with the treatment of EoE. We learn the differences in FeNO-levels in patients with EoE with and without comorbidities (asthma and rhinitis) and control subjects. In conclusion, although FeNO-levels are elevated in patients with EoE, they do not help diagnose or evaluate treatment response. They could be more beneficial to rule out the disease if FeNO-levels are as low as the negative predictive value is high. The subjects without asthma and FeNO-l > 30 parts per billion are likely to suffer EoE, especially if they have symptoms of esophageal dysfunction or swallowing disorders.

Acknowledgment: None

Declaration of conflict of interest

All of the authors who have contributed to this work declare NO conflicts of interest.

Funding Source: None

This work has not been funded by anything or anyone.

Presentations of This Work: This Work Has NOT Been Previously Presented To Any Congress Or Scientific Meeting, Nor Has It Obtained Any Award Or Mention

Patient Consent Statement

All patients, parents, and guardians gave us written permission to participate in the study, and the Ethics Committee later approved this study of the Hospital.

Authors' Contribution to the Manuscript

AR Gratacos: Made substantial contributions to the conception, design of the study, and writing of the article M Clar: Made substantial contributions in the data acquisition JR Muñoz: Participated in the histological analysis and interpretation of the data J Joyanes: Realization of the study tables JV Meneses: Search of the bibliography E Gomez: Supervision and submission of the manuscript All the authors have reviewed all the patients during the years of the study.

1. Godwin B, Wilkins B, Muir AB. EoE disease monitoring: Where we are and where we are going. Ann Allergy Asthma Immunol. 2020; 124: 240-247.
2. Barni S, Arasi S, Mastrorilli C, Pecoraro L, Giovannini M, Mori F, et al.Pediatric eosinophilic esophagitis: a review for the clinician. Ital J Pediatr. 2021; 22; 47:230.
3. Leung J, Nguyen-Traxler A, Lee EM, Yip JS, Weinstock JV, Chan WW, et al. Assessment of fractionated exhaled nitric oxide as a biomarker for the treatment of eosinophilic esophagitis. Allergy Asthma Proc. 2012; 33:519-24.
4. Xu F, Zou Z, Yan S, Li F, Kan H, Norback, et al. Fractional exhaled nitric oxide about asthma, allergic rhinitis, and atopic dermatitis in  Chinese  J Asthma.  2011;48:1001-1006
5. Ulrik CS, Lange P, Hilberg O. Fractional exhaled nitric oxide as a determinant for the clinical course of asthma: a systematic review. Eur Clin Respir J. 2021; 8:1891725.
6. Dweik RA, Boggs PB, Erzurum SC, Irvin CG, Leigh MW, Lundberg JO. American Thoracic Society Committee on Interpretation of Exhaled Nitric Oxide Levels (FENO) for Clinical Applications. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FENO) for clinical applications. Am J Respir Crit Care Med. 2011 Sep 1; 184: 602-15.
7. Chen FJ, Huang XY, Liu YL, Lin GP, Xie CM. Importance of fractional exhaled nitric oxide in the differentiation of asthma-COPD overlap syndrome, asthma, and COPD. Int J Chron Obstruct Pulmon Dis. 2016; 11:2385-2390.
8. Kawasumi T, Takeno S, Ishikawa C, Takahara D, Taruya T, Takemoto, et al. The Functional Diversity of Nitric Oxide Synthase Isoforms in Human Nose and Paranasal Sinuses: Contrasting Pathophysiological Aspects in Nasal Allergy and Chronic Rhinosinusitis. Int J Mol Sci. 2021; 22:7561.
9. Dellon ES, Liacouras CA, Molina-Infante J, Furuta GT, Spergel JM, Zevit N, et al. Updated International Consensus Diagnostic Criteria for Eosinophilic Esophagitis: Proceedings of the AGREE Conference. Gastroenterology. 2018; 155: 1022-1033.
10. Eifan AO, Durham SR. Pathogenesis of rhinitis. Clin Exp Allergy. 2016 ;46:1139-1151
11. Hines BT, Rank MA, Wright BL, Marks LA, Hagan JB, Straumann A, et al. Minimally invasive biomarker studies in eosinophilic esophagitis: A systematic review. Ann Allergy Asthma Immunol. 2018;121: 218-228.
12. Pijnenburg MW, Hofhuis W, Hop WC, De Jongste JC. Exhaled nitric oxide predicts asthma relapse in children with clinical asthma remission. Thorax. 2005;60:215-218
13. Nakamura Y, Hashiba Y, Endo J, Furuie M, Isozaki A, Yagi K. Elevated exhaled nitric oxide in anaphylaxis with respiratory symptoms. Allergol Int. 2015; 64:359-63.
14. O?wi?cimska J, Ziora K, Ziora D, Machura E, Smerdzi?ski S, Py?-Spycha?a M, et al. Elevated levels of exhaled nitric oxide in patients with anorexia nervosa. Eur Child Adolesc Psychiatry. 2014;23:845-850
15. Badar A, Salem AM, Bamosa AO, Qutub HO, Gupta RK, Siddiqui IA. Association Between FeNO, Total Blood IgE, Peripheral Blood Eosinophil and Inflammatory Cytokines in Partly Controlled Asthma. J Asthma Allergy. 2020; 13:533-543.
16. Johnson K, Iyer V, Katzka D, Ravi K, Lennon R, Pendegraft R, et al. Poor Relationship Between Fractionated Exhaled Nitric Oxide and Disease Activity in Eosinophilic Esophagitis. Dysphagia. 2019; 34:138-144.
17. Dor-Wojnarowska A, Liebhart J, Grabowski M, Czapla L, Grabowski K, Panaszek B. St??enie tlenku azotu w wydychanym powietrzuu chorych na zapalenie prze?yku [Exhaled nitric oxide in patients with esophagitis]. Pneumonol Alergol Pol. 2011;79:272-277
18. Kiljander TO, Laitinen JO. The prevalence of gastroesophageal reflux disease in adult asthmatics. Chest. 2004;126:1490-494
19. Silvestri M, Mattioli G, Defilippi AC, Fregonese B, Battistini E, Jasonni V, et al. Correlations between exhaled nitric oxide levels and pH-meter data in asthmatics with gastro- oesophageal reflux. Respiration. 2004; 71: 329-35.
20. Gomez Torrijos E, Gonzalez-Mendiola R, Alvarado M, Avila R, Prieto-Garcia A, Valbuena T, et al. Eosinophilic Esophagitis: Review and Update. Front Med (Lausanne). 2018; 5:247.
21. Lucendo AJ, Molina-Infante J, Arias A, von Arnim U, Bredenoord AJ, Bussmann C, Guidelines on eosinophilic esophagitis: evidence-based statements and recommendations for diagnosis and management in children and adults. United European Gastroenterol J. 2017; 5: 335-358.
22. Capucilli P, Hill DA. Allergic Comorbidity in Eosinophilic Esophagitis: Mechanistic Relevance and Clinical Implications. Clin Rev Allergy Immunol. 2019; 57: 111-127.
23. Antosova M, Bencova A, Mokra D, Plevkova J, Pepucha L, Buday T. Exhaled and Nasal Nitric Oxide - Impact for Allergic Rhinitis. Physiol Res. 2020; 69: 123-130.
24. Yoon J, Choi YJ, Lee E, Cho HJ, Yang SI, Kim YH, et al. Allergic Rhinitis in Preschool Children and the Clinical Utility of FeNO. Allergy Asthma Immunol Res. 2017; 9: 314-32.
25. Lanz MJ, Guerrero RA, Gonzalez-Vallina R. Measurement of exhaled nitric oxide in evaluating eosinophilic  esophagitis  in    Ann  Allergy  Asthma  Immunol.  2012; 109:81-82.
26. Heffler E, Carpagnano GE, Favero E, Guida G, Maniscalco M, Motta A. Fractional Exhaled Nitric Oxide (FENO) in the management of asthma: a position paper of the Italian Respiratory Society (SIP/IRS) and Italian Society of Allergy, Asthma, and Clinical Immunology (SIAAIC). Multidiscip Respir Med. 2020; 15:36.